xii OOGENESIS 569 



divide and give rise to the egg-mother-cells, or female 

 gametocytes, which do not immediately undergo division, 

 but remain passive and increase in size by the absorption 

 of nutriment from surrounding parts : in this way each 

 egg-mother-cell gives rise to an ovum. Sometimes this 

 nutriment is simply taken in by diffusion or osmosis, or 

 by means of protoplasmic connection between the ovum 

 and the follicle-cells ; in other cases the growing ovum 

 actually ingests neighbouring cells after the manner of 

 an Amoeba, i Thus in the developing egg the processes 

 of constructive are vastly in excess of those of destructive 

 metabolism. 



We have seen (p. 249) that the products of destructive 

 metabolism may take the form either of waste products 

 which are got rid of, or of plastic products which are 

 stored up as an integral part of the organism. In the 

 developing egg, in addition to the increase in the bulk 

 of the protoplasm itself, a formation of plastic products 

 usually goes on to an immense extent. In plants the 

 stored-up materials may take the form of starch, of oil, 

 or of proteid substance : in animals it consists, as men- 

 tioned above, of rounded or angular grains of proteid 

 material, known as yolk-granules. These being de- 

 posited, like plums in a pudding, in the protoplasm, have 

 the effect of rendering the fully- formed egg opaque, so 

 that its structure can often be ma.de out only in 

 sections. 



Before, however, the ovum is ripe for conjugation 

 with a sperm or able to undergo the first stages of 

 segmentation it has to go through a process known as 

 maturation, which consists essentially in a twice repeated 

 process of cell-division, and thus resembles the process 

 just described in the case of the sperms. 



Let us take a case, as before, in which the number of 

 chromosomes characteristic of the species is twelve. 



PRACT. ZOOL. N N 



