CHAP, i.] FEMALE ORGANS. 357 



appearance of granules in a secreting cell . the ovum transforms 

 and deposits in itself in the form of yolk granules for future use 

 the surplus material which it receives from the tollicle One 

 purpose of the zona radiata appears to be to afford mechanical 

 protection to the ovum, but it also probably exercises some 

 influence on this transmission of material ; and in this respect 

 the likeness which it presents to the striated border of the villi 

 of the intestine is suggestive. Outside the zona radiata between 

 it and the cells of the cumulus may be more or less distinctly 

 recognized a layer of granular material which, secreted apparently 

 by the cells of the cumulus, seems to be the analogue of the 

 albumen or ' white ' of the hen's egg. We know little definite 

 concerning the nature of the fluid tilling the ripe tollicle, but it 

 is probably of the nature of lymph ; in ovarian cysts, which are 

 abnormal developments of follicles, special forms of proteids have 

 been found. 



932. The growth of a follicle from its earliest phase onwards 

 consists then, partly in an increase in the ovum itself; the cell- 

 substance ot this becomes larger and increasingly loaded with 

 yolk, the nucleus or germinal vesicle and its nucleoli or germinal 

 spots become increasingly conspicuous, and during part of the time 

 the zona pellucida acquires increasing thickness ; but the growth 

 also consists in an enlargement of the walls of the follicle and 

 an increase of the cells of the membrana granulosa, as well as in 

 a distension of the enlarging follicle by fluid which appears to be 

 secreted by those cells. 



In an ordinary epithelium, such as that of the skin or mucous 

 membrane, each constituent cell is nourished by the lymph which 

 reaches it from the blood vessels of the underlying dermis. and 

 each cell influences or is influenced by its fellows only so far as to 

 secure that all the cells should work together in due order. In the 

 germinal epithelium certain cells, namely the ova, acquire special 

 properties and are set apart tor a special end. By the introduc- 

 tion of what special material, or by the bringing to bear of what 

 special influences they are thus set apart, is a problem too wide 

 for us to consider here ; they are thus set apart. And it would 

 appear that having been thus set apart, they pursue a career 

 different from that of other cells. They do not multiply in the 

 same simple way that other cells multiply ; as far as can be ascer- 

 tained, the number of ova in an ovary is early established, and not 

 subsequently increased. And their nutrition is of such great value 

 that the lives of neighbouring cells are devoted to securing it ; 

 the ordinary cells of the germinal epithelium surrounding an 

 ovum are told off to nourish it, and so form the membrana granu- 

 losa of a follicle. The nutritive assistance given by these sub- 

 sidiary cells is twofold : they secrete the lymph-like follicular 

 fluid, by which the ovum is indirectly nourished ; and those cells 

 which form the cumulus appear to convey material in a more 



