454 DEVELOPMENT OF ELASMOBRANCH FISHES. 



and the epithelium of the throat ; but the two are so close 

 together, that I am inclined to think that such a junction still 

 exists. It is certainly present up to stage P. 



Dr MUller 1 , in his exhaustive memoir on the thyroid body, 

 gives an account of its condition in two Acanthias embryos. In 

 his earliest embryo (which, judging from the size, is perhaps 

 about the same age as my latest) the thyroid body is discon- 

 nected from the throat, yet contains a lumen, and is not divided 

 up into lobules. It is clear from this account, that there must 

 be considerable differences of detail in the development of the 

 thyroid body in Acanthias and Scyllium. 



In the Bird Dr Muller's figures shew that the thyroid body 

 developes in the region of the hyoid arch, whereas, in Elasmo- 

 branchs, it developes in the region of the mandibular arch. 

 Dr Gotte's 2 account of this body in Bombinator accords very 

 completely with my own, both with reference to the region in 

 which it developes, and its mode of development. 



The pancreas. 



The pancreas arises towards the close of stage K as a some- 

 what rounded hollow outgrowth from the dorsal side of that 

 part of the gut which from its homologies may be called the 

 duodenum. In the region where the pancreas is being formed 

 the appearances presented in a series of transverse sections are 

 somewhat complicated (PL 18, fig. i), owing to the several parts 

 of the gut and its appendages which may appear in a single 

 section, but I have detected no trace of other than a single out- 

 growth to form the pancreas. 



By stage L the original outgrowth from the gut has become 

 elongated longitudinally, but transversely compressed : at the 

 same time its opening into the duodenum has become some- 

 what narrowed. 



Owing to these changes the pancreas presents in longitudinal 

 and vertical section a funnel-shaped appearance (PL 19, fig. 4). 

 From the expanded dorsal part of the funnel, especially from 

 its anterior end, numerous small tubular diverticula grow out 



1 Jenaische Zeitsckrift, Vol. vi. 



2 Entwicklungsgeschichte d. Unke. 



