456 DEVELOPMENT OF ELASMOBRANCH FISHES. 



the Elements of Embryology, p. 133, and also with the results 

 of Gotte on the Amphibian liver. Schenk has thrown doubts 

 upon the hypoblastic nature of the secreting tissue of the liver, 

 but it does not appear to me, from my own investigations, that 

 this point is open to question. 



Coincidently with the formation of the hepatic network, the 

 umbilical vein (PI. II, fig. 9, u. v.) which unites with the sub- 

 intestinal or splanchnic vein (PI. n, fig. 8 V.) breaks up into a 

 series of channels, which form a second network in the spaces 

 of the hepatic network. These vascular channels of the liver 

 appear to me to have from the first distinct walls of delicate 

 spindle-shaped cells, and I have failed to find a stage similar to 

 that described by Gotte for Amphibians in which the blood- 

 channels are simply lacunar spaces in the hepatic parenchyma. 



The changes of the median duct of the liver are of rather a 

 passive nature. By stage O its anterior end has dilated into 

 a distinct gall-bladder, whose duct receives in succession the 

 hepatic ducts, and so forms the ductus choledochus. The duc- 

 tus choledochus opens on the ventral side of the intestine im- 

 mediately in front of the commencement of the spiral valve. 



It may be noted that the liver and pancreas are correspond- 

 ing ventral and dorsal appendages of the part of the alimentary 

 tract immediately in front of its junction with the yolk-sack. 



The subnotochordal rod. 



The existence of this remarkable body in Vertebrata was 

 first made known by Dr Gotte 1 , who not only demonstrated its 

 existence, but also gave a correct account of its development. 

 Its presence in Elasmobranchs and mode of development were 

 mentioned by myself in my preliminary account of the devel- 

 opment of these fishes 2 , and it has been independently ob- 

 served and described by Professor Semper 3 . No plausible 

 suggestion as to its function has hitherto been made, and it is 

 therefore a matter of some difficulty to settle with what group 



1 Archivfur Micros. Anatomic, Bd. V., and Entwicklungsgeschichte d. Unke. 



2 Quarterly Journal of Microscopic Science, Oct, 1874. [This Edition, No. V.] 



3 " Stammverwandschaft d. Wirhelthiere u. Wirbellosen " and " Das Urogenital- 

 system d. Plagiostomen," Arb. Zool. Zoot. Jnstitut. z. Wiirsburg, Bd. ri. 



