EMBRYOLOGY OF THE SEA BASS, 
235 
! a matter for surprise. They probably in the end lose their identity and are absorbed 
as so much food material. Certainly there is no ground for believing (in the Bass) 
: that they become blood corpuscles. 
Historical . — In pelagic eggs the alimentary canal has usually been supposed to 
j originate as a solid thickening of the entoderm lamella (Ryder 34, Kingsley and Conn 
' 28, Agassiz and Whitman 1, Cunningham 8). Cunningham concluded that the ventral 
i part of the thickening (floor of canal) was formed from periblastic elements, which 
migrated out of the yolk ; but the grounds for this conclusion were very inadequate. 
'' The formation of the canal in the trout has been studied in greater detail. From 
I Oellacher’s paper (33) it is difficult to arrive at a decision as to its exact mode of forma- 
tion. Hoffmann (17), however, distinctly states that the process is one of folding, but 
: aside from the branchial region his description is scarcely detailed enough to give one 
I a satisfactory idea of the matter. Ziegler (48) and Henneguy (18) both describe the 
I canal as arising in the main as a fold, and compare the process with the correspond- 
: iug phenomenon in the Amuiota. Henueguy’s description is the more detailed of the 
! two, and is no doubt in the main accurate for the trout. According to Henneguy, in 
the anterior part of the trunk behind the branchial region the canal is formed as a 
! thickening which subsequently becomes hollow. In the rest of the trunk there is a 
j median fold, the walls of which are so appressed that the cavity is a virtual one, 
Henneguy, however, does not sjjeak of the postanal gut, aud believes that the cavity 
of Kupffbr’s vesicle is continuous with that of the intestine : ‘‘ Lavesicule de Kupff'er 
I n’est done que la premiere apparition de la cavite du tube digestif avec laquelle elle se 
i confond plus tard” {1. c., p. 563, Fig. 109, PI. xxi). This can scarcely be so, for 
[ Schwarz’s sections (39) prove the presence of a solid postanal gut in the trout, which 
i subsequently atrophies together with Kupffer’s vesicle. * 
\ K^ipfferh vesicle . — The discovery of this vesicle was made by Kupff’er in 1868 (24), 
j and since then it has occupied a conspicuous place in the embryology of Teleosts. Its 
formation has never been satisfactorily worked out, aud it has hence given rise to 
[ more discussion than could justly be claimed by it. The discoverer of the vesicle 
j believed that it arose as an ectodermic invagination from the dorsal surface (25, 26), 
I and in his figures the vesicle is shown as such a sac, closed below and opening on the 
dorsal Surface, In his general scheme of vertebrate gastrulation Kupff'er makes this 
sac play an important part. He regards it as homologous with the dorsal invagination 
of Eeptilia, which he believes (26) constitutes the allantois (and part of rectum). The 
vesicle is then, for Kupff'er, a structure which in higher groups becomes the allantois. 
From this standpoint it is a little misleading to speak of it as a rudimentary allantois, 
as is commonly done. It is rather a prophetic ” allantois. However, no one has 
ever confirmed Kupffer’s account of the way in which the vesicle is formed, aud until 
that is done it would scarcely seem possible to entertain any homology between the 
vesicle and the invagiuated pit of reptiles. 
Other investigators who have discussed this point of Teleost development depart 
widely from Kupff'er’s account, but differ among themselves. On the one hand Kings- 
ley and Conn (28), Agassiz and Whitman (1), Cunningham (9), state that the vesicle 
arises as a space between the entoderm proper aud the periblast. Henneguy (18) 
and Schwarz (39), on the other hand, contend that from the start the vesicle has a 
cellular floor, and arises as a closed cavity amongst the cells in front of the caudal 
mass. It will be noticed that the former group of investigators all worked on pelagic 
