XIII 



PHYLUM CHORDATA 



11 



drawn out into a sort of" stalk on which the buds are devi.' loped 

 (Fig. 712). A pair of ovaries (ov.) lie in the trunk-cavity, and 

 there is a pair of oviducts (ovd.) (originally su])})osod to be eyes) 

 lined by elongated, pigmented epitlieliuni. The development. 



f :'■ 



'^ '■'/.'-. -^ ^i^^^J^^- '-^y /-^ 



•■1l 







-^ 



J 



Fio. 712.— Cephalodiscus. Entire zooid. (After Mcintosh.) 



which is direct, without free-swimming larval stage, takes place 

 in passages in the investment. According to one account the 

 segmentation is complete, but unequal, and a gastrula is formed 

 by invagination : according to another, the segmentation is in- 

 complete, and a gastrula is formed by delamination. 



