10 OOGKENESIS 



cell. It consists of a nuclear membrane enclosing a clear material or matrix, 

 imbedded within which may sometimes be seen strands of karyoplasm ; it always 

 encloses one or more well-marked nucleoli (fig. 15). Frequently there is but one 

 nucleolus, which is then large and prominent, and has received the name of 

 germinal spot (macula germinativa, Wagner, 1835). 



In the young oocyte (fig. 17) there is a body (idiosome) near the nucleus, corre- 

 sponding to the attraction- sphere of other cells. It encloses a central granule, and 

 is itself surrounded by a mass of fine granules (mitochondria). Van der Stricht 

 identifies 'his body with the yolk-nucleus or body of Balbiani. 1 There are also 

 other cell-inclusions to which various names have been given, but it is doubtful 

 what significance they possess. 



Oog-enesis, The earlier stages of oogenesis and the development of the 

 Graafian follicle will be treated of under the head of the ovary. Here we shall 



begin with a stage m which the young egg-cell 

 is already imbedded in the developing gland, 

 and surrounded by a layer of follicular cells. 



It will be recollected that the spermatozoa are derived 

 from the spermatogonia lining the testicular tubules, and 

 that the first phase is characterised by marked and 

 comparatively rapid growth of the spermatocytes. The 

 process begins at puberty and proceeds continuously 

 throughout the greater part of the life of the individual. 

 The young egg- cells or oogonia, on the other hand, have 

 all become converted into oocytes by the time of birth. 

 These undergo a very slow process of growth and ripening, 

 FIG. 17. YOUNG OOCYTE SUB- anc i are discharged singly at periodic intervals during 



JCVer - *T * hort P- M of -productive activity. 



Stricht.) 



Showing attraction - sphere, centre- As the oocyte grows the Graafian follicle is 



some, and mitochondria. gradually enlarged. The follicular cells, at first 



laid down as a single layer (fig. 17), multiply to 



form a many-layered investment to the ovum. By the formation of fluid among 

 them (fig. 18) the cells come to bound a cavity into which, from one part of 

 the wall, a cellular mass projects surrounding the egg (the discus proligerus). 

 The cells of the discus proligerus are arranged in an epithelial fashion 

 round the ovum, and remain in intimate relationship to it during the process 

 of ripening. 



The oocyte is not at first provided with a zona pellucida, and the manner in 

 which this develops has not yet been quite cleared up. Authorities differ as to 

 whether it is formed by the follicular cells or is a true egg-membrane secreted 

 by the ovum. 



maturation of the oocyte ; formation of the polar bodies. By the 

 term c maturation ' is signified the series of changes which prepare the egg for 

 fertilisation. During a very prolonged period of growth the deutoplasm becomes 

 gradually accumulated in the protoplasm. The phenomena observed during this 

 period have been recently described for the human ovum in great detail by 

 Van der Stricht.' 2 From this it would appear that the mitochondria, which are 

 regarded as specific cytomicrosomes, are concerned in the elaboration of the yolk. 

 They first collect round the idiosome, then become scattered, arrange themselves 

 in chains (chondriomites), solid rods (pseudo-chromosomes), and irregular bodies ; 

 later they become arranged in double rows to form minute tubules, which extend 



1 See also Gurwitsch, Archiv f. mikr. Anat. Ivi. 1900; and Winiwarter, Archives de Biologie, xvii. 

 1900. 



2 Loc. cit. 



