XIII 



PHYLUM CHORDATA 



11 



drawn out into a sort of stalk on which the buds are developed 

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

 there is a pair of oviducts (ovd.) (originally supposed to be eyes) 

 lined by elongated, pigmented epithelium. The development, 



Fifi. 712. Cephalodiscus. Entire zooid. (After Mclntosh.) 



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. 



