520 THE AXATOMY OF LNVEETEBRATED ANIMALS. 



CM 



Fig. \A^.—Phalhma mam7niUata.—Yar\ons stages in the development of the larvae. 

 (After Kowalewsky.')! 



I. The ve?i( ular morula, flartencd and about to undergo invagination :/A, blastocoele. 

 The large blastomeres constitute the hypoblast, the Bmall ont-s the epiblast. 



II. The L'astrnla with the blastopore, or opening of invagination, eo: ch, the blasto- 

 mere? which constitute the rudiment of the urochord; (Id, the remaining blasto- 

 meres of the hvpoblast. 



III. A more advanced embryo: ch, dd, as before; c. the epiblast; n, the nervous 

 layer of ttie neural cavitv. which is now open only in front near ch. 



IV. An embryo with the caudal appendage distinct. The nerve-tube n is complete, 

 and the muircle-cells m are distinguishable. 



^"Weifcre Rtudien liher die Entwickelung der einfachen Ascidien." 

 (" Archiv fur Mikr. Anat.," 1871.) 



