190 WILLIAM WAI,LACE. 



tlielium is a single layer of small uuiform cells as iu all other 

 species. The large nutritive cells make their appearance at 

 a very early stage in the development of the follicle (fig. 28). 

 In this case it is not easy to say whether we have two oocytes 

 in a follicle, one of which — to the left — has taken the lead, or 

 whether the large cell to the right of the figure is a nutritive 

 cell derived from the follicular epithelium. The resemblance 

 to oocytes of these large nutritive cells is very striking, and 

 suggests interesting considerations. Semper went so far as 

 to say that the larger cells in such follicles were probably 

 primitive ova destined to become permanent ova. Schultze 

 (1875) thought the large cells in the follicular epithelium of 

 Torpedo were leucocytes. 



Figs. 29 and 30 are sections of the follicular epithelium and 

 adjacent structures in Chimasra monstrosa. Fig. 30 shows 

 the condition of the epithelium and egg membrane towards 

 the vegetable pole. Fig. 29 is a section nearer the animal 

 pole. This distinction between animal and vegetable poles 

 becomes well marked, both in Spinax and Chima^ra, at a 

 very early period in the growth of the oocytes, and is initiated 

 by the migration of the germinal vesicle to one end of the 

 egg. I have noticed in botli species that it is invariably to 

 the same side that the nucleus travels, viz. to that end which 

 is diametrically opposite to the area of attachment of the egg 

 to the surface of the ovary. In other words, the animal pole 

 is always directed inwards, towards the substance of the 

 ovary. Whether the direction of migration of the germinal 

 vesicle has any relation to the source of nutrient supply I 

 cannot definitely say, but it is worth remarking that in the 

 substance of the ovary both of Spinax and Chimasra there is 

 a great development of lymph spaces. Further, each follicle 

 is surrounded by a lymph space, except on the side where 

 the follicle is attached to the ovarian wall. It may be that 

 the nucleus travels to that side which is most favourably 

 situated for access to the lymph. 



The polarity of the egg in vSpinax and Chimasra is also 

 manifested in the difference in the condition of the follicular 



