42 



PHYLUM TUNIC ATA (UROCHORDA). 



en. 



FIG. 35. Two stages in the development of Pyrosoma (after Kowalevsky from Korschelt and 

 Heider). In A the yolk of the ovum is partly surrounded by the cyathozooid c which has 

 developed on it (see Fig. 34) ; in B the yolk is entirely enclosed by the cyathozooid. c cyatho- 

 zooid, d its atria! pore, d its alimentary canal, do its yolk ; ec ectoderm ; el elaeoblast (a 

 mesoblastic mass in the buds) ; en endostyle of ascidiozooid ; ft ciliated pit and g ganglion 

 of cyathozooid ; i mouth, ks gill-slits of ascidiozooid ; I vascular space of cyathozooid ; 

 m test ; n ganglion of ascidiozooid ; p peribranchial (atrial) cavity of ascidiozooid ; sn lateral 

 nerve ; v endodermal canal connecting ascidiozooids ; z mesoblast cells. 



C 



cc. 



FIG. 36. Three stages in the development of the proliferating stolon of Pyrosoma (from Kor- 

 schelt and Heider, after Seeliger). In C the division of the stolon into two buds, I and II. 

 is indicated, d pharyngeal process (epicardium) ; ec ectoderm ; es endostyle of parent ; 

 (i genital (mesoderm) band ; ks first gill-slits ; m rudiment of digestive cana'l ; n rudiment 

 oi neural tube. 



