470 



which lie in the twelve pairs of ovarian tubules begin to 

 undergo a series of changes, which transform them into 

 mature ova. A consideration of the nuclear changes is 

 beyond the scope of this paper; I shall confine my description 

 to the more obvious changes in the cells. 



The oogonia in the distal part of the tubules divide 

 actively (without any centrosome, so far as I could observe) ; 

 those in the proximal part of the tubes cease to divide and 

 arrange themselves in little balls, which pass down the tubes 

 (fig. 189) and eventually enter the four channelled oviducts. 

 The grouping up of the cells into these little balls can be 

 clearly observed at the point between the region of irregularly 

 arranged cells and that at which the last ball has been 

 formed. No difference is at this stage visible in any of the 

 cells of any of these little masses (fig. 189). Very soon, how- 

 ever, changes begin. The central cell of every alternate 

 group begins to grow; it is the future ovum, and the sur- 

 rounding cells form the follicle; the balls of cells on either 

 side of these developing ova are the groups of nutritive cells. 



The follicle cells at first do not undergo any appreciable 

 changes. The ovum, however, is soon characterized by a 

 quickly growing nucleus. The nutritive cells soon increase in 

 size; indeed, by the time the fourth group of cells is forming, 

 the nutritive cells of the first have already grown to llfx in 

 diameter. The egg meanwhile grows rapidly, but though it 

 probably develops at the expense of the follicle and nutritive 

 cells, these do not appear to suffer greatly; the follicle cells 

 maintain a remarkable constancy in size. When the egg has 

 reached a diameter (it is now slightly oval) of 12ju,, the follicle 

 cells are still 5/x to G/x in diameter; they have, however, 

 become somewhat cubical instead of rounded in shape, so as 

 to form a more complete covering for the ovum. 



When the egg reaches a length of 52^, the first polar 

 body is formed; it is very large, measuring some lO'Syi, in 

 diameter, and is clearly seen lying beneath the follicle cells 

 (fig. 190). Even now, however, the follicle cells have not 

 diminished appreciably in size; indeed, although the ovum is 

 probably living partly at their expense, they may actually 

 show an increase in size, reaching at times a thickness of 7/ui. 



The behaviour of the nuclei of the nutritive cells, how- 

 ever, is quite different. The nucleus grows greatly in size 

 and may reach a diameter of 5ju; the chromatin is scattered 

 regularly throughout it, and is no longer contained in a 

 karyosome. 



Eventually, however, the follicle cells also begin to grow, 

 but the growth of the nuclei never ceases. When the ovum 



