THE EGG 



somewhat staggering, but not altogether preposterous, for 

 we have good reason to think that some other very important 

 cells, e.g. the chief cells of the brain and spinal cord, last a 

 whole lifetime without replacement. Other anatomists think 

 they can see scraps of evidence that new crops of eggs are 

 continually being formed in the ovary of the adult woman, 

 and that these new eggs are those which are shed from the 

 ovary in adult life. It is well known that the male germ cells 

 are formed anew continuously in adult animals (see Chapter 

 IX). The question, as regards the ovary is (for technical 

 reasons) much more difficult to solve than it might seem. I 

 have myself studied it quite seriously in a large collection of 

 monkey ovaries, and thus far have not seen good evidence that 

 new formation of eggs occurs. For this reason I adhere cau- 

 tiously to the old view until new evidence is brought forward. 



At any rate, some of the eggs in the reserve zone are from 

 time to time selected to proceed to maturity. Such an egg 

 sinks deeper into the ovary. The cells about it multiply to 

 form a thick mass, which soon hollows out to form a small 

 follicle. As the cavity enlarges, the egg is left in its little 

 hillock at one side (Plate VII, A, B,C). 



Discharge of the egg. The follicle continues to grow and to 

 occupy more and more space, slowly shoving aside neighbor- 

 ing tissues within the ovary. Finally it enters a period of very 

 rapid growth, so that its volume doubles in a few hours. Plate 

 VIII shows the growth of the follicle in the rat. The human 

 follicle becomes 12 or 15 millimeters (0.5 to 0.6 inch) in 

 diameter when fully developed and occupies at least one- 

 fourth of the whole volume of the ovary. As it enlarges, it 

 pushes its way to the surface. The wall of the follicle next the 



Plate VI. De Graafs original illustration of the Graafian follicles, in the 

 ovary of the cow, from De organis generationem inservientibus, 1672. A large 

 follicle is shown at B, smaller ones at C, C, C, C. E is & large follicle dissected 

 away from the ovary. The lower portion of the figure shows the oviduct 

 (Fallopian tube) with its funnel-like expansion. Approximately natural size. 



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