66o PATTERNS AND PROBLEMS OF DEVELOPMENT 



Hertwig, 1880). The Phialidiutn oocytes are almost pedunculate (Fig. 

 212, C, D), and the oocytes of some anthozoa do become pedunculate 

 at relatively early stages. 



PEDUNCULATE DEVELOPMENT 



Oocytes of many invertebrates become pedunculate sooner or later in 

 the growth period. The peduncle may develop from a regional attach- 

 ment of the oocyte itself or from follicular or other cells. The oocytes 



A B 



Fig. 213, A, 5.— Early and full-grown oocyte of Sternaspis sciUaia, the early stage showing 

 the blood vessel at the attached pole (from Child, 19156). 



are primarily cells of an epithelium ; development of a peduncle is associ- 

 ated with their growth and protrusion into the ovarian cavity. An ex- 

 treme case of pedunculate development appears in the gephyrean Sternas- 

 pis. The peduncle attains considerable length, and a blood vessel extends 

 throughout its length, forming a loop in the cytoplasm of the attached 

 pole of the oocyte (Fig. 213, ^). From an early stage on, the nucleus lies 

 at the free pole (Fig. 213, 5), the polar bodies form there, and it becomes 

 the apical pole of an embryo with spiral cleavage. 



Echinoderm oocytes show various degrees of peduncle development, 

 ranging from regional attachment with little elongation to peduncles of 

 considerable length. In the case of the sea urchin the attached pole be- 



