520 THE ANATOMY OF IXVERTEBRATED ANIMALS. 



Chk 



Fig. I40.—Phann.<nam(77vjninafa.~-Ycinon& stashes in the development of the larvaj. 



C After Kowalewsky.^i 

 I. The vesicular morula, flattened and about to undergo invagination :fh. hlastoccele. 



The large blastomeres conetitnfe the hypoblast, the small one? the epihlapt. 

 n. The gastnila with the blastopore, or opening of invagination, eo: en, the blasto- 



mere? which conctitnte the rudiment of the urochord; dd, the remaining blasto- 



meres of the hypoblast. 

 ni. A more advanced embryo: ch, dd, a? before; c. the epiblast ; n, the nervous 



layer of the neural cavity, which is now open only in front near ch. 

 rV". An embryo with tlie caudal appendage distinct. The nerve-tube n is complete, 



and the mu:^cle-cells m are distinguishable. 



* ""Weitere Studicn fiber die Entwickelung der einfachen Ascidien." 

 (" Archiv furMikr. Anat.," 1871.) 



