SKIN GRAFTS IN THE LIZARD, ANOLISCAROLINENSIS, CUV.

BY RAOUL M. MAY.

{Zoological Laboratory, Harvard University.')

WITH TWO PLATES.

i. Introduction.

T H E large amount of work on skin grafts in vertebrates hasconcerned itself for the most part with either amphibians ormammals. I have been able to find only one recorded case ofskin grafting in reptiles. It is that of Winkler (1910) onLacerta. However, his account is not very clear concerningthis lizard. He simply states that he used skin from thethroat region for the graft, and does not give the subsequenthistory of the transplant, but includes whatever results heobtained along with those reported for amphibians.

W. H. Cole (1922) has recently summarised the evidenceconcerning the specificity of skin transplants and the migrationof melanophores in transplanted skin, including both autotrans-plants and homoiotransplants. From his own observations onfrog tadpoles, supplemented by the earlier report of Schone(1912), he has come to the conclusion that in frog tadpoles,mice, and human beings autotransplants show a local specificityof integument. He says (p. 406) that in frog tadpoles theintegument is " locally specific, and is self-differentiating whentransplanted to new soil on the same animal."

Nevertheless, he reports that in frog tadpoles white bellyskin grafted on to the back, whether in autotransplants orin homoiotransplants, eventually acquires melanophores. Thisagrees with the results obtained by Winkler (1910) on frogsand tadpoles, and with those of Dawson (1920) in autotrans-plants on Necturus maculosus. With guinea-pigs a similarpigmentation of white grafts on a black region was reportedby Loeb (1897) and by Seelig (1913)-

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Raoul M. MayEvidence concerning the reactions of pigmented grafts on

a white region is not so clear. Dawson (1920) reported thatan autotransplant on Necturus maculosus, after several weeks,became lighter at its centre, the area of lightening extendingcentrifugally. The light appearance was due to the absence ofthe usual dermal chromatophores, as the epidermal chromato-phores were still present. Carnot et Deflandre (1896) notedthat in both autotransplants and homoiotransplants onguinea-pigs the graft persists and the pigment invades thesurrounding white skin when the graft is made on animalswhich have some pigmented areas on their coats, but itdisappears if skin from a pigmented animal is grafted on toalbinos. Loeb (1897) a^s0 reported the spreading of pigmentfrom the black graft to the surrounding white skin of guinea-pigs, while Sale (1913), repeating Loeb's experiments, foundthat this occurred only in autotransplants ; homoiotransplantsbecame gradually lighter in colour.

To determine the reactions of highly specialised chromato-phores to transplantation, I chose the so-called Florida orAmerican chameleon, Anolis carolinensis, Cuv. This lizardoffers several points of great value in this connection. As iswell known, its skin can go through a fairly wide range ofcolour phases, the most common and conspicuous of whichare an emerald green and a mahogany brown. These changeswere first described by Lockwood (1876), and the histology ofthe skin was worked out by Carlton (1903), but especially wellin the masterful paper of von Geldern (1921). Anolis, in itspigmentation, differs greatly from those forms on which skingrafting had been done previously. Loeb and Strong (1904)have pointed out that in the frog skin there are two layers ofchromatophores, one dermal, the other epidermal, while in theguinea-pig the cutis has no well-developed chromatophores,and its pigment is distributed irregularly in layers or clumps.In Anolis, on the other hand, there are no epidermalchromatophores, and the dermal melanophores are highlyspecialised. Instead of branching irregularly in severaldirections, as is usually the case, they have dendritic processeswhich are always directed toward the epidermis. Whateverthe secondary factors may be in the colour changes, both

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Skin Grafts in the LizardCarlton (1903) and von Geldern (1921) have conclusively shownthat the main change is a migration of the pigment granulestoward the epidermis to produce the brown state, while acellulipetal movement of the pigment granules produces thegreen state.

While working on the main problem, several collateralquestions arose, and I have incorporated the work which I puton them into the present paper.

I take great pleasure in acknowledging here my debt ofgratitude to Professor H. W. Rand, at whose suggestion thework was begun, and under whose inspiring guidance it wascarried on.

2. Material and Methods.

Animals were procured from a dealer in New Orleans.They were kept in a thermostat chamber at a temperature of23.50 C. At this temperature the animals thrive if the air inthe chamber is kept humid. This is best accomplished bykeeping a wet sponge in the vivarium. The sponge is usedalso as a drinking supply, since the lizards take wateronly in the form of droplets. They were given insectsfor food.

Ansesthetisation was found to cause so many fatalitiesthat it was discarded. In operating, all antiseptic precautionsmust be taken, as the lizards are very liable to infection.The areas of skin which were to be cut out were first markedwith india ink, so that the graft would fit as closely aspossible into the area which was to receive it. Pieces of skin0.3 to 0.8 centimetre square were used, and reciprocal graftswere usually made, whether autoplastic or homoioplastic. Thebest results were followed when the edges of the skin to begrafted were applied closely to the edges of the skin at theplace of reception. This was sometimes difficult. The skinof Anolis is connected with the underlying muscles only by avery loose layer of connective tissue, so that when cut thereis little resistance to its tendency to shrink, and the area forreception of the graft becomes often much larger than desired.After applying the smoothed-out graft, a very little celloidinwas placed on the edges, both to hold the graft and to prevent

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Raoul M. Mayinfection. The operative shock caused the lizards to be veryquiet for several hours. This lapse of time was enough toallow the celloidin to harden completely, and for a vascularsupply to be established for the grafts.

Lizards of various sizes, but apparently all adult, were usedfor the experiments. I was successful in thirty-one cases ofgrafting. Of these, twenty-one were autotransplants and tenwere homoiotransplants.

3. Autotransplants.

a. Pigmented Grafts on a White Region.—In Anolis, as inmany reptiles, the under side of the body contains very fewmelanophores, so that the venter and throat are whitish.Some individuals do show a very slight change in shade ofthe under side when the animal changes colour. This shadingappears as an extremely light green when the lizard is green,and a very light brown when it is in the brown state. In mostindividuals, however, this does not occur, so that the venterand throat are whitish when the animal is in either the brownor the green state. In the following descriptions, I shall usethe term "pigmented skin " to mean that portion of integumentcontaining numerous melanophores.

In the first series of experiments pigmented skin from theback or sides of the body was grafted on to the belly or throat.The results are the same in all cases.

When the patch to be grafted is cut from the surroundingskin and is pulled up from the subcutaneous connective tissueit becomes immediately either green or brownish green, if thelizard when operated on is in the brown state. If, however,the lizard is in the green phase during the operation, then thepatch remains green. The brownish - green colour of theisolated skin, when it occurs, is only transitory. Ten to fifteenminutes after the patch is attached to its place of reception, itis always bright emerald green. Furthermore it has completelylost the power to change from green to brown. The restof the integument retains the capacity of colour change, sothat in the brown state the graft stands out in strong contraston the white belly or throat as a green area (fig. 1), while theback and sides of the lizard are brown.

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Skin Grafts in the LizardWhen the graft "takes," a vascular supply for it is

established within a few hours. A graft for which a bloodsupply is not established becomes wrinkled and soon dies.The fact that such a supply exists in the case of successfultransplants can be easily ascertained by pulling up one of theircorners. The area under it is richly bathed in blood. Never-theless the graft remains green for days, and is unaffected bythe changes in colour of the animal as a whole. In severalcases some of the scutes of the graft, or even a good portion ofit, acquired a straw yellow colour after two or three days.This colour, however, did not change when the animal asa whole changed, but seemed to be static, like the remaininggreen colour of the transplant.

I examined my grafted animals daily to determine the firstappearance of the brown state in the grafted skin. Thiscomes on very gradually, and its mode of appearance variessomewhat in different lizards. Usually beginning twenty ortwenty-one days after the operation, a few of the scutes—asa rule, two or three at one edge of the graft—are found tobe brown when the animal as a whole is brown, andsynchronously become green when it becomes green. Inthe following days more of the scutes acquire this capacity.The area within the graft reacquiring the power of colourchange grows very irregularly and with no definite pattern.Twenty-four to thirty-three days after the operation the entiregraft has fully acquired the power to change from green tobrown, and vice versa, with all the intermediate colours, and itdoes so synchronously with the animal as a whole.

After the reacquisition of the capacity for colour changein the graft, there is no further change. The pigmented skintransplanted to a region with no melanophores now behavesin exactly the same way that it did when it was in its normalplace on the back or side of the lizard.

The specificity of the integument is complete. There isno invasion of the surrounding white skin by the melanophores,and the line of demarcation between pigmented and whiteareas of the integument remains perfectly definite. Lizardswhich were observed for seven months showed at the endof that time as sharp a line of distinction between the graft

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Raoul M. Mayand the surrounding skin as on the day of the operation(figs- 3. 5)-

As von Geldern (1921) has noted, different areas of theintegument have scutes of different shapes and sizes. Withoutgoing into the details of these differences, for which thereader is referred to von Geldern's paper, it can be statedthat there has never been the slightest change in the appear-ance of back skin when transplanted to an area on the bellyor throat. The scutes of transplanted back or side skin caneasily be distinguished from the surrounding larger and moreclosely arranged scutes of the venter, or from those of thethroat skin where there are wide spaces between the scutes.

To ascertain whether the change of position of the skinon the animal had anything to do with the behaviour whichit subsequently underwent, pieces of skin were cut out andreplaced on the same area from which they had been excised.The resulting changes in colour behaviour were exactly ofthe same nature as when integument was transplanted toanother area of the body.

There is, then, no influence of the surrounding skin uponthe graft. It shows exactly the same changes whether it issurrounded by pigmented or by white skin.

b. Experiments on the Nervous Control of the Melanophores.—Carlton (1903) injected solutions of nicotine into Anolis topoison the sympathetic ganglia. A result was the changeof brown animals to green. Isolated pieces of skin in whichthe brown state had been induced by mechanical stimulationwere permeated with a nicotine solution, but did not becomegreen. He showed that the spinal nerves were not concernedwith the colour changes, since these took place after pithingthe spinal cord. He concluded that the effect of the nicotinewas not on the melanophores directly, but through thesympathetic nervous system. Since poisoning the sympatheticganglia with nicotine produced the green state, he postulatedthat the brown state is ordinarily maintained through a tonusestablished by the sympathetic nerves. Fuchs (1914, p. 1648)has questioned this result, claiming that it is not proven thatnicotine does not have a direct effect on the chromatophoresor on their nerve supply, irrespective of the ganglia.

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Skin Grafts in the LizardThe present experiments afford added evidence in support

of Carlton's contention. By grafting a piece of skin, wedestroy all its nerve connections and thereby abolish thefunction of the nerve endings. It is true that so far therehas been no anatomical proof of the existence of nerve endingsin relation to the melanophores of Anolis. Von Geldernfailed to get them by the chloride of gold method; I failedlikewise, using the methods of Golgi and of Bielschowsky.But that nerve endings, such as Ballowitz (1893) anc* Eberthund Bunge (1895) demonstrated for the chromatophores offishes, exist likewise in the melanophores of Anolis, seemsalmost certain. The sudden change of excised skin to thegreen state, and the fact that a vascular supply fails to bringback the colour-changing reaction, are indications of a nervouscontrol. But the best evidence for it is in the gradualregaining of full function by the melanophores, a changewhich can be correlated only with the slow regeneration ofnerves.

Hooker (1912a) found that a three and a half months' oldregenerated tail in Lacerta agilis was innervated by two pairsof nerves which had grown out from the stump of the tail.These nerves, which normally innervated about 2 mm. of thetail, now took care of the whole 30 mm. of regenerated tip.Whether, in the case of skin grafts, the new innervation ofthe melanophores is a result of an extension of the nervesfrom the skin surrounding the graft, or whether the newinnervation is by nerves growing up through the subcutaneousconnective tissue is, of course, not proven. It is likely,however, that as in Lacerta, it is the nerves from the immediatevicinity which extend into the new region. In the case ofa pigmented patch on the venter, we have the curious exampleof nerves which had supplied a region where almost nomelanophores were present, growing into skin with numerousmelanophores, and assuming then the colour-changing functionwhich up to that time they had exercised either not at all,or at most only in very small degree.

In order to determine whether in Anolis the melanophoresare supplied by nerves going vertically up to them through thesubcutaneous tissue, or whether the innervation is by a plexus

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Raoul M. Maywhich joins all portions of the integument, two types ofexperiment were performed. In the first a sharp scalpel wasinserted under the dermis in a pigmented area, and a smallarea of integument was wholly separated from the underlyingtissues, thus severing any nerves which came to the skin fromthat direction. However, excepting the incision made by theinsertion of the scalpel, there was no separation from thesurrounding skin. The animals were operated on while inthe brown state. The results of this experiment showed somevariation, but in general the cases were similar. Usually theseparated skin immediately became green, but in some cases itremained brown for several hours. After a day, in bothinstances, the operated area was composed of irregular blotchesof green and yellow, with usually some brown scutes. Thegreen and yellow spaces, as time went on, became more andmore restricted, so that after four or five days the operatedarea was totally brown when the lizard was in the brown state.

The other experiment consisted in leaving the area of skinattached to the subcutaneous tissue, but cutting it off fromthe surrounding skin. In this case, the severing of relationswith the surrounding integument seemed to have little effecton the melanophore control. The cut area was brown whenthe animal was in that state, and changed colour synchronouslywith the rest of the skin. The only change that could benoticed was that sometimes there appeared patches on theedges of the area somewhat lighter brown than the remainingintegument.

If the two operations were combined, so that three or fourdays after the separation of an area of skin from the under-lying connective tissue, this same area was also isolated fromthe surrounding skin, it immediately turned green andremained so. The further changes, with the reacquisition ofthe colour-changing capacity, were the same as those notedfor transplants of pigmented skin. The reapparition of thebrown colour came on in the same irregular and slowfashion.

We see, then, that three conditions were observed. Whena portion of the integument was separated from the sub-cutaneous tissue alone it became green, then blotched, and

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Skin Grafts in the Lizardregained the capacity of colour change within four or five days.When an area of skin was separated from the surroundingintegument, but not from the subcutaneous layer, no importantchange occurred ; the area showed normal colour behaviour.When finally an area which had been separated from thesubcutaneous layer, and had regained the power of colourchange, was subsequently cut off from the surrounding skin,it became green and reacquired completely normal behaviouronly twenty-four to thirty-three days later.

What the factors are which operate in these conditions Iam unable to say with certainty. It seems, however, that thesurrounding skin can exert some influence in bringing aboutthe normal state in an area lacking most of its innervation.This is shown by the fact that such an area which hadregained the capacity of colour change loses it when separatedfrom the neighbouring integument.

From these experiments, I feel that we are justified inconcluding that—

1. The normal innervation of the melanophores is largelyfrom nerves which reach them directly from beneathand not through a plexus in the skin.

2. Any melanophore-bearing portion of the skin isolated,by incision, from surrounding skin but with itssubcutaneous layer intact, can act normally withthe rest of the integument in its colour changes.

3. An area whose direct (i.e., subcutaneous) innervationhas been cut off regains, after a delay of three tofive days, control of its melanophores, apparently byacquiring some relation with the surrounding skin.

c. The Effect of Adrenalin on Grafts.—Redfield (1918) hasstated that injections of adrenalin brought about the greenstate of the skin in Anolis carolinensis. It seemed to me ofinterest to determine whether the effect would be the same ongrafts which had fully regained their colour-changing power.To test this question I injected o. 1 c.c. of a solution made upof one part of adrenalin chloride in either 1000, or else 100,000,of Ringer's solution, subcutaneously into lizards which were inthe brown state. One and a half to two minutes after the

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Raoul M. Mayinjection the animal as a whole and the graft had both turnedgreen. There is then no difference as regards the reaction toadrenalin between normal skin and grafts.

That the effect of adrenalin in the case of the melanophoresof Anolis is not directly upon them, but indirectly throughthe sympathetic nervous system was well shown. Skin wascut out, placed on filter paper bathed with Ringer's solution,and mechanically stimulated so as to bring it into the brownstate, as Carlton had done. If now a solution made up ofadrenalin, one part in either iooo or 100,000 of Ringer'ssolution, is added, so that the brown skin is bathed in it,there is no change in the coloration, even after an immersionof one hour's duration. The state induced by mechanicalstimulation persists so that the skin remains brown, or atmost shows only such minor changes in its colour as arealso shown by controls bathed merely in Ringer's solution.

Two lizards upon which pigmented skin had been trans-planted several months previously had their spinal cordpithed. They were allowed to recover from the operativeshock for two hours; the graft as well as the rest of thepigmented skin became brown. Adrenalin was then injected,and the usual change to green was shown by both the graftand the melanophore-bearing integument.

The effect of adrenalin in causing the proximal migrationof the pigment granules in the melanophores, in pigmentedgrafts as well as upon normal skin, is shown as a resultof these experiments to take place indirectly through thesympathetic nervous system. These results agree with thoseof Carnot (1897) on the frog. He notes that section of thespinal cord did not inhibit the colour changes of the skinin the paraplegic portion of the animal. Isolated portionsof the skin failed to show their normal colour changes whentreated with drugs. Thus, detached . light skin failed todarken when bathed in amyl nitrite, and dark skin failed tolighten when treated with aniline hydrochloride. In thecase of skin normally attached to the animal, however, amylnitrite causes a centrifugal movement of the pigment granulesin light skin, while aniline hydrochloride causes a centripetalmovement of the granules in dark skin. These drugs, as in

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Skin Grafts in the Lizardthe case of adrenalin in Anolis, can produce their effect onthe melanophores of the frog only through the action of intactsympathetic nerves.

d. White Grafts on a Pigmented Region.—Skin taken fromthe white venter or throat and grafted on to the pigmentedsides or back of an Anolis shows a strict specificity. Lizardsobserved for six and a half months did not show during thattime the slightest evidence of blending of the grafts with thesurrounding skin. The line of demarcation between the whitegraft and the surrounding skin was absolute (figs. 2, 4, 6).There was not the slightest indication of migration of melano-phores into the white graft, and the latter was in no wayinfluenced by the surrounding skin. The highly specialisedmelanophores of Anolis have apparently lost the power ofmigration which is possessed by the chromatophores ofamphibians and at least some mammals. As in the caseof pigmented grafts, the white transplants showed a strictspecificity as regards the region from which they were taken.Belly skin retained the characteristic larger scutes, while throatskin could easily be recognised by the wide intervals betweenthe scutes, and by its loose connection with the subcutaneoustissues. The other characteristics of the scutes from thedifferent regions of the lizard's body, such as shape and thepresence or absence of a central keel, were also retainedunchanged.

It appears, therefore, that both pigmented and white skin,when transplanted autoplastically to regions of the oppositekind, retain their own characters. Lacerta likewise (Winkler,1910) shows a specific character of different portions of theintegument. Furthermore in Anolis the melanophores haveno power of movement independently of the nervous system,such as Hooker (1912<$) found in the melanophores of thecorium of Rana fusca, nor is there, in the lizard, any evidenceof migration of any kind.

4. Homoiotransplants.a. Transplants.—With one notable exception, all homoio-

transplants were absorbed, although they usually " took" atfirst. The following data, taken from my notes, on a white

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Raoul M. Maygraft transferred to the back of another Anolis, illustratethe usual run of events.

1923.

March 1. A graft 0.6 cm. square was transferred from the belly of Anolis 59to the back of Anolis 60.

March 15. The graft, normal in appearance, is firmly established and is wellhealed.

April 4. The celloidin around the edges of the graft has been sloughed oflas a consequence of ecdysis. The scutes of the graft are allwhite and in perfect shape.

April 18. 25 scutes on the graft have become dull grey, and appear thinnerand less opaque than they were.

May 2. The graft shows irregular areas where there are no scutes, butonly a dull grey superficial layer. Other irregular areas stillshow the scute formation, but the scutes have become dullgrey. Some scutes show only partial absorption, remainingwhite in half or a quarter of their area, the rest being grey.

May 11. Only 160 scutes on the graft are either completely or partly white.May 19. Only 86 scutes remain white totally or partially. Over the rest of

the graft appears a dull grey superficial layer.May 29. There has been a total disappearance of the white scutes. Only a

dry superficial layer shows traces of the original scales. Thislayer easily peels off, and under it is a soft grey membraneshowing only a very indistinct outline of where the scuteshad been.

June 8. The vague outline of the scutes has disappeared from the greymembrane. The latter now appears smooth.

The interval of ninety days here reported between thegrafting operation and the total absorption of the scutes issomewhat longer than usual. The interval in the other caseswas from sixty-one to seventy-seven days. Pigmented skintransferred to the venter of another lizard was absorbed in thesame way as white skin, and in about the same time.

In only one case of homoioplastic grafting did I get resultsunlike those described above. One lizard which had whiteskin from another. Anolis grafted on to its back, and skinfrom the other animal's back grafted on to its belly wasobserved for four months. During that time there was notthe least indication of absorption. The grafts healed well.The white graft did not differ from an autoplastic graft ofthe same character. The pigmented graft, however, neverreassumed complete colour change. Two and a half months

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Skin Grafts in the Lizardafter the transplantation irregular areas of the graft, or eventhe greatest portion of it, had assumed a light brown colourquite distinct from the deeper brown of the animal as a whole.These light brown areas showed synchronous change to greenwith the rest of the pigmented integument. They were not,however, constant in position on the graft, but changed fromday to day, or even temporarily disappeared from it. Thegraft would then appear green, mottled with straw yellow, inthe brown state of the animal. This graft thus showedstriking differences from other pigmented transplants, bothautoplastic and homoioplastic.

The Anolis from which the grafts were taken in this casewas of exactly the same size as the recipient. Both camefrom New Orleans in the same lot. There is, then, thepossibility that I was, in this instance, dealing with syngenesio-transplants. This would perhaps explain why the behaviourof the graft was different from that of both autotransplantsand homoiotransplants.

In general, my homoioplastic cases showed, as before noted,complete destruction of the grafted skin after an interval offrom sixty to ninety days. These results differ markedly fromthose of Winkler (1910) on Lacerta and amphibians. He saysthat " Es spielt dabei keine Rolle, ob die zur Transplantationverwendeten Hautstiickchen von demselben Tiere stammen,oder ob die Haut eines andern Tieres benutzt wird."

b. The Growth of Scales.—As has been noted, absorbedhomoiotransplants were replaced by a grey membrane. Whenautotransplants were accidentally thrown off, a grey membrane,presumably new integument, likewise was seen covering thesurface. These membranes showed ecdysis along with therest of the integument.

The somewhat similar phenomenon of scute regenerationoccurring when the lizard breaks its tail and regenerates a newone led me to compare the growth of scutes in both situations.In the case of regenerated tail tips, the first outgrowth is ablackish cone, covered by thin, smooth skin. When thisundergoes ecdysis, the scutes are found completely formedunderneath, and very regular in shape and size.

The mode of regeneration of scutes on the back or belly

Raoul M. Maydiffers from that on the tail. Wherever scuteless integumenthas replaced a graft, whether after absorption of homoio-transplants, or to cover open wounds, after two or two anda half months there can be noticed on the edges of theregenerated integument a formation of new scutes. These,as fig. 7 shows, are very irregular in shape and size, some

FIG. 7.—Regeneration of scutes on area denuded of skin three and a halfmonths previously, x 17.

being larger than normal scutes, while others are muchsmaller. When surrounded by pigmented skin the regeneratedscutes are copper-coloured, and show no change of colour whenthe animal changes. In white areas they are white. In bothcases we find that at successively later stages of scute regenera-tion they are found nearer the centre. After five months theyhave completely invaded the area formerly denuded of scales.They are then pressed close together, having lost the inter-spaces which characterised them at first. The white scales

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Skin Grafts in the Lizardblend in very well with the surrounding skin, but the copper-coloured regenerated scutes never have, in my experience,acquired the colour-changing capacity.

We see, then, that the regenerated scutes differ in pigmenta-tion according to whether they appear near melanophore-bearing or white integument. The fact that these scutesalways appear first at the edges of the old skin seems tojustify the belief that the neighbouring old skin has a directinfluence in their regeneration.

5. Summary.

1. Autotransplants of pigmented (melanophore-bearing)skin on a white region, and of white skin on a pigmentedregion both exhibit a strict specificity.

2. There is no migration of the melanophores in any caseof transplantation.

3. Transplants of pigmented skin lose their colour-changingpower immediately on being completely disconnected fromneighbouring tissues, and regain it slowly as nerves regenerate.

4. The melanophores are supplied largely by nerves whichreach them directly through the underlying tissues. If thesenerves are cut from a given area of skin, without separatingthe area from the surrounding skin, it at first loses the powerof colour change, but the neighbouring integument appearsable, after a delay of a few days, to control the denervatedarea.

5. Areas of melanophore-bearing skin, isolated by incisionfrom surrounding skin, but with their subcutaneous connectionsintact, can act normally with the rest of the animal in thecolour-changes.

6. Adrenalin, in producing the green state in pigmentedgrafts which have regained the colour-changing function, actsas it does upon normal integument. The action is indirectlythrough the sympathetic nervous system, and not directlyupon the melanophores.

7. Homoiotransplants, either pigmented or white, areabsorbed. The absorption occurs after the grafts have wellhealed in place. The scutes disappear, leaving the areacovered by thin scaleless integument.

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Raoul M. May8. New scutes regenerate wherever there are areas barren

of them. Scute regeneration progresses centripetally, suggest-ing some formative influence exerted by the surroundingnormal integument.

The photographs for this paper were kindly taken for meby Mr E. C. Cole, and the coloured plates were made byMr E. N. Fischer.

6. References.Ballowitz, E. (1893), "Die Nervenendigungen der Pigmentiellen, ein Beitrag zur

Kenntnis des Zusammenhanges der Endverzweigungen der Nerven mit demProtoplasma der Zellen," Zeitf. wiss. Zool., 66, 673-706, 5 pis.

Carlton, F. C. (1903), "The Color Changes in the Skin of the So-called FloridaChameleon, Anolis carolincnsis, Cuv." Proc. Amer. Acad. Arts and Sci., 39,257-76, 1 pi.

Carnot, P. (1897), " Recherches sur le mdcanisme de la pigmentation," Bull. Set'.,France et Bdg., 80, 1-82, 2 pis.

Carnot, P., et Deflandre, Cl. (1896a), "Persistence de la pigmentation dans lesgreffes ^pidermiques," Mem. Soc. BioL, 8, ioeme se>ie, 48 (coll.), 178-80.

Carnot, P., et Deflandre, Cl. (1896*), "Greflfe et pigmentation," Mem. Soc. BioL, 8,ioeme se'rie, 48 (coll.), 430-32.

Cole, W. H. (1922), "The Transplantation of Skin in Frog Tadpoles, with SpecialReference to the Adjustment of Grafts over Eyes, and to the Local Specificityof Integument," Journ. Exp. Zool., 36, No. 4, 353-419, 4 pis.

Dawson, A. B. (1920), "The Integument of Necturus waculosus," Journ. Morph., 84,486-589, 6 pis.

Eberth und Bunge, R. (1895), "Die Nerven der Chromatophoren bei Fischen,"Arch./, mik. Anat, 46, 370-78, 2 pis.

Fuchs, R. F. (1914), "Der Farbenwechsel und die chromatische Hautfunktion derTiere," Handbuch vergl. Physiol. Herausg. von Hans Winterstein, 8, Halfte r,Teil 2, 1189-1656.

von Geldern, C. E. (1921), "Color Changes and Structure of the Skin of Anoliscarolinensis," Proc. Calif. Acad. Set., 4th Series, 10, No. 10, 77-117, pis. 7-9.

Hooker, D. (1912a), "Die Nerven im regenerierten Schwanz der Eidechsen," Arch.f. mikr. Anat., 80, Abt. 1, 217-22.

Hooker, D. (1912*), "The Reactions of the Melanophores of Rana fusca in theAbsence of Nerve Control," ZeiUf. allg. Physiol., 14, 93-104, 3 figs.

Lockwood, S. (1876), "The Florida Chameleon," Amer. Nat., 10, No. 1, 4-16.Loeb, L. (1897), "Ober Transplantation von weisser Haut auf einem Defekt in

schwarrer Haut und umgekehrt am Ohx des Meerschweinchens," Arch. Ent.-Mech., 6, 1-44, 3 pis.

Loeb, L., and Strong, R. M. (1904), "On Regeneration in the Pigmented Skin ofthe Frog, and on the Character of the Chromatophores," Amer. Journ. Anat,8, 275-83-

Redfield, A. C. (1918), "The Physiology of the Melanophores of the Horned ToadPhrynosoma," Journ. Exp. Zool., 28, No. 2, 275-333, 5 pis.

Sale, L. (1913), "Contributions to the Analysis of Tissue Growth. VIII.—Auto-plastic and Homoeoplastic Transplantation of Pigmented Skin in Guinea-pigs,"Arch. Ent.-Mech., 87, 248-58.

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SKIN GRAFTB IN TUB LIZARD.— RAOOL M. MAY.

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Skin Grafts in the LizardSch6ne, G. (1912), "Die heteroplastische und homboplastische Transplantation,"

Eigene UnUrsuchungen und vergleichende Studien, Berlin. Cited after Cole,W. H., 1922.

Seelig, M. G. (1913), " Contributions to the Analysis of Tissue Growth. IX.—HomS-oplastic and Autoplastic Transplantation of Unpigmented Skin in Guinea-pigs,"Arch. Ent.-Mech., 87, 259-64.

Winkler, F. (1910), " Studien iiber Pigmentbildung. I.—Die Bildung der verzweigtenPigmentzellen im Regenerate des Amphibienschwanres. II.—Transplanta-tionsversuche an pigmentierter Haut," Arch. Ent.-Mech., 29, 616-31, 4 pis.

7. Description of Plates.FIG. 1.—Autotransplant of back skin to belly, three months after operation ; green

state, x 15.FIG. 2.—Autotransplant of belly skin to back, three months after operation, x 15.FIG. 3.—Autotransplant of back skin to belly, two months after operation ; brown

state. Life-size.FIG. 4.—Autotransplant of belly skin to back, three months after operation.

Life-size.FIG. 5.—Autotransplant of back skin to throat, five months after operation ;

brown state. Life-size.FIG. 6.—Autotransplant of throat skin to back, five months after operation.

Life-size.

555