HABITS, ETC., OP CEREBRATULUS LACTEUS. 123 



derm o£ the intestine grows out to tlie right and left between 

 the pillars and along the side of the muscle walls, thus form- 

 ing the intestinal cseca. A blood-vessel, connecting the 

 dorsal with the latei*al vessels, is formed in the connective 

 tissue at the inner end of each csecum (hv.). The genital 

 pouches are thus bordered anteriorly and posteriorly by 

 bands of dorso-ventral muscles, above by the proboscis 

 sheath, and below by the lateral blood-vessel beneath the 

 intestine. 



An epithelium now appears, made up of small irregular 

 nucleated cells which cover the pouch unevenly. It is 

 impossible for this epithelium to be formed by an outgrowth 

 from either the ectoderm or entoderm, since it nowhere 

 comes in contact with either of them. It is evidently 

 derived from the parenchymal tissue which binds together 

 the vertical muscles to form the wall of the ovary or testis. 



In winter the pouches are much smaller than the caeca, 

 and are flattened between the latter until their sides meet. 



Early in spring the sexual products begin to develop, 

 appearing first at the outer end of the pouch nearest the 

 muscles of the body-walls. In the figure given (fig. 63) it 

 will be seen that the pouch extends, in the form of separate 

 longitudinal pockets, both forward and backward along the 

 ends of the adjacent caeca (cf. figs. 61 and 62). 



Oogenesis. — The first appearance of egg development is 

 an increase in one of the nuclei of the epithelium lining these 

 pouches. This is carried so far that the nucleus with its 

 large nucleolus comes to occupy a large portion of the cell. 



It is then gradually surrounded by a layer of fine-grained 

 protoplasm which protrudes into the lumen of the pouch 

 (ec.', fig. 65). 



Subsequent development consists in a continued growth of 

 both cell body and nucleus, the latter developing into the 

 large germinal vesicle and the former spreading somewhat 

 over the adjacent epithelium cells which have remained 

 apparently unchanged (ec"). This gives the ovum a flask 

 shape, the neck of the flask being inserted between the epi- 



