279

The Continuity between the Cavities of the PremandibularSomites and of Rathke's Pocket in Torpedo

By SIR GAVIN DE BEER, F.R.S.(Correspondant de Vlnstitut de France; Director of the British Museum {Natural History))

SUMMARY

The existence of an open communication between the cavity of Rathke's pocketand the cavity of the premandibular somite in Torpedo ocellata at the 7 mm. stage isdemonstrated by means of microphotographs. They provide a complete refutation ofthe claim by B. Wedin that because he was unable to find continuity of open com-munication between the cavities of Rathke's pocket and of the premandibular somite,therefore E. S. Goodrich was mistaken in homologizing the preoral pit of Amphioxuswith the hypophysis of craniates. On the contrary, Goodrich's observations are con-firmed and his theory vindicated.

IN his paper on the connecting strands between the premandibular cavitiesand Rathke's pocket, B. Wedin (1951) stated that E. S. Goodrich (1917)

and I (de Beer, 1925, 1926) had based his 'theory' that the preoral pit ofAmphioxus was homologous with the cavity of the hypophysis or Rathke'spocket of craniates, on A. Dohrn's (1904) descriptions of embryos of Torpedo,and that he (and I) had misunderstood them. In particular, Wedin claimedthat Dohrn's expression 'Verbindungen' in his description of the conditionsin Torpedo had been mistranslated by Goodrich, and erroneously interpretedto mean that Dohrn had observed continuous hollow connexions between thecavities of the premandibular somites and that of Rathke's pocket. Wedinhas re-examined Dohrn's material of Torpedo and found no continuous hollowconnexions, but only strands of cells connecting the premandibular cavitieswith Rathke's pocket in which occasional lumina are present.

If Wedin had read Goodrich's and my papers with sufficient attention hewould have seen that we based our 'theory' not on Dohrn's descriptions, buton our own positive observations in Torpedo of uninterrupted connexionsbetween the cavities of the premandibular somites and of Rathke's pocket ofwhich we published figures. We found this condition to be variable and thehollowness of the connexion transient. The discovery of the hollow connexionin Torpedo was made by Dr. Elizabeth Fraser in material belonging to J. P.Hill. This material was studied by Goodrich, and Dr. Fraser's observationconfirmed and figured (Goodrich, 1917, text-fig. 36, and pi. 28, fig. 15).

In my paper (de Beer, 1925, p. 103) I described observations that I hadmade on material of Torpedo which I had prepared myself, and wrote 'Zuerststehen die pramandibular Somite und die Hypophyse in offener Verbindung',and gave a figure of a section of an embryo in text-fig. 17, illustrating thisfact. In my book (de Beer, 1926) I repeated this in fig. 91, p. 72. Both Goodrich(1917, p. 548) and I (de Beer 1926, p. 35, fig. 31) were able to confirm theexistence in Anas of a connexion with an obvious obliterated virtual lumen.

[Quarterly Journal of Microscopical Science, Vol. 96, part 2, pp. 279-283, 1955.]

dpsL

eR

p in

ps

r

LRpr

Rp

FIG

. I.

A-H

, mic

roph

otog

raph

s of

eig

ht co

nsec

utiv

e se

ctio

ns th

roug

h an

em

bryo

of

Tor

pedo

oce

llat

a, 7

mm

. lon

g (s

erie

s A

,sl

ide

1, ro

w 4

, sec

tions

20-

27.

G.

R. d

e B

.—D

.C.A

. , O

xfor

d).

Pho

tos

by M

. G

. Sa

wye

rsam

, ang

le o

f m

outh

; cp

s, c

ellu

lar

stra

nd c

onne

ctin

g le

ft a

nd r

ight

pre

man

dibu

lar

som

ites;

csl

, cel

lula

r st

rand

con

nect

-in

g le

ft pr

eman

dibu

lar

som

ite t

o ep

ithel

ium

of

Rat

hke'

s po

cket

; cs

r, c

ellu

lar

stra

nd c

onne

ctin

g ri

ght

prem

andi

bula

r

som

ite to

epi

thel

ium

of

Rat

hke'

s po

cket

; dps

l, de

pres

sion

in

wal

l of

left

prem

andi

bula

r so

mite

; dp

sr, d

epre

ssio

n in

wal

lof

rig

ht p

rem

andi

bula

r so

mite

; eR

p, e

pith

eliu

m o

f R

athk

e's

pock

et;

in,

post

erio

r w

all

of i

nfun

dibu

lum

; Ip

p, o

pen

left

prob

osci

s po

re;

IRp,

left

div

ertic

ulum

of

Rat

hke'

s po

cket

; m

sl,

cavi

ty o

f le

ft m

andi

bula

r so

mite

; pc,

pha

ryng

eal

cavi

ty;

psl,

cavi

ty o

f le

ft pr

eman

dibu

lar

som

ite; p

sr, c

avity

of

righ

t pr

eman

dibu

lar

som

ite; r

Rp,

rig

ht d

iver

ticul

u m o

f R

athk

e's

pock

et;

Rp,

cav

ity o

f R

athk

e's

pock

et.

282 de Beer—The Continuity between the Cavities of the

Dohrn's work was referred to by Goodrich together with that of otherauthors, because they had observed connexions between the premandibularsomites and the hypophysis in Torpedo, Raia, Phrynocephalus, Gongylus, andAnas, and these connexions, whether solid or hollow, were obviously homo-logous with the hollow connexions which we have observed in Torpedo.

Wedin has been at some pains to prove that Dohrn's material shows nocontinuous hollow connexions between the premandibular cavities and thehypophysis, and has reproduced photomicrographs of four embryos ofTorpedo, most of which show in the connecting strand of cells a lumen whichWedin asserts does not extend right through. I have no intention of contestingWedin's descriptions of Dohrn's material. It is difficult to prove a negativeproposition, and to invalidate Wedin's argument I only need to reproducemicrophotographs of an embryo showing that the hollow connexion betweenthe premandibular cavities and Rathke's pocket is a fact.

The embryo is one of Torpedo ocellata, 7 mm. long, cut into horizontalsections, 10 ju. thick (series A, slide 1, row 4, sections 20-27 in the Departmentof Zoology and Comparative Anatomy, Oxford). Fig. 1, A, shows a sectionthrough the most anterior morphological level of the series. The posteriorwall of the infundibulum is seen cut tangentially, in contact ventrally withthe thickened epithelium of the anterior portion of Rathke's pocket. On eachside of the infundibulum is a premandibular somite with a large cavity. Thesomite on the left is almost in contact with the epithelium of the left diverti-culum of Rathke's pocket; that on the right is a little way distant.

Fig. 1, B, which is of the next section, 10 JJL farther back, shows that the leftpremandibular somite has come into closer contact with the epithelium ofRathke's pocket and that the cavity of the somite shows a conical depressionin its wall immediately over the point of contact.

Fig. 1, c, shows the open pore between the cavity of the left premandibularsomite and the cavity of Rathke's pocket. The limiting membrane of thelining of the cavity of the somite is perfectly continuous with the membraneof the lining of the cavity of Rathke's pocket. The 'proboscis-pore' is open,and its diameter in the transverse plane is approximately 10 /x, which is aboutthe same as its diameter in the sagittal plane, since the open pore is also plainlyvisible in the next section, shown in Fig. 1, D, at a level 10 fx farther back.

In fig. 1, E, the connexion between the left premandibular somite andRathke's pocket is no longer open, but the wall of the right premandibularsomite is seen to approximate to the epithelium of Rathke's pocket on thatside. Rathke's pocket itself now appears as a closed cavity since the section istaken dorsally to its communication with the pharyngeal cavity.

Fig. 1, F, shows that the right premandibular somite is intimately connectedwith the epithelium of Rathke's pocket, and cone-shaped depressions can beseen in the walls of the cavity of the somite and of the right diverticulum ofRathke's pocket, immediately at the point of contact. The pore is not open onthis side.

In the next section, fig. 1, G, the connexion between the right somite and

Premandibular Somites and of Rathke's Pocket in Torpedo 283

Rathke's pocket is still intimate, and the cone-shaped depression is also presentin the wall of the cavity, but it is no longer seen in the wall of Rathke's pocket.In fig. 1, H, the right somite and Rathke's pocket are still in contact, and thestrand can be seen connecting the left and right premandibular somites acrossthe middle line.

In the light of these facts I challenge Wedin's statement (1951, p. 75):'Leider machte Goodrich dabei einen Fehler und unterstellte Dohrn Beobach-tungen, welcher dieser nicht gemacht hatte. Dieser Irrtum durfte aussch-laggebende Bedeutung fur die Gedanken Goodrich's haben.' Goodrich madeno such mistake, nor that of drawing conclusions from facts which he hadnot observed himself. His hypothesis that the preoral pit of Amphioxus ishomologous with the hypophysis of craniates, and that the open connexionsbetween the premandibular cavities and Rathke's pockets represent 'pro-boscis-pores', remains unshaken. It might be added that it would still beunshaken if the connexions were solid, for it is a commonplace of comparativeanatomy and of embryology that homologous structures may arise or remainsolid, or hollow, and so no morphological significance can be ascribed to suchdifferences.

In a subsequent paper, Wedin (1952) has described an open connexionbetween the cavities of the premandibular somite and of Rathke's pocket inTorpedo.

REFERENCESDE BEER, G. R., 1925. 'Die Geschichte der Pars tuberalis der Pituitardriise.' Anat. Anz.,

60, 97.1926. The comparative anatomy, histology, and development of the pituitary body. London

(Oliver & Boyd, 1926).DOHRN, A., 1904. 'Studien zur Urgeschichte der Wirbeltiere. 24. Die Pramandibularhohle.'

Mitt. Zool. Stat. Neapel, 17, 1.GOODRICH, E. S., 1917. ' "Proboscis pores" in craniate vertebrates, a suggestion concerning

the premandibular somites and hypophysis.' Quart. J. micr. Sci., 62, 539.WEDIN, B., 1951. 'Die Verbindungsstrange zwischen den Pramandibularhohlen und der

Rathke'schen Tasche.' Proc. Akad. Sci'. Amst., 54, 75.1952. 'Tissue bridges and tubular connections between the premandibular cavities

and Rathke's pouch.' Ibid., 55, 416.