THE PROCESS OF FERTILIZATION 



301 



cell lies in the fact that the divisions of the so-called ' spermatocyte ' 

 or mother-sperm-cell are equal, so that four granddaughter-cells of 

 equal size arise, while in the mother-egg-cell or 'ovocyte' the 

 divisions are very unequal. In the former the result of the divisions 

 is four cells capable of fertilizing, in the latter one cell capable of 

 being fertilized and three minute 'polar cells' which are incapable 

 of conjugating with a sperm-cell and giving rise to a new individual. 



There can thus be no doubt that the polar cells, as Mark and 

 BUtschli long ago suggested, are abortive ova, that is, that, at a 



JiedE 



Fig. 77. Diagram of the maturation-divisions of the sperm-cell, adapted from 

 0. Hertwig. A, primitive sperm-cell. B, mother-sperm-cell. C, first maturation 

 division. D i and 2, the two daughter-cells. E, the second maturation division, by 

 which the four cells of F arise, each with half the number of chromosomes. 



remote period in the evolution of animal life, each of these four 

 descendants of a mother- egg-cell became a germ-cell capable of 

 development. It is not difficult to infer that the unequal division, 

 which now leads to an insufficient size in three of these descen- 

 dants, has gone on ^jcmy i^ssil with the continually inci'easing size 

 of the mature ovum, and had its reason in the fact that it was 

 important above all things to store in the ovum as much protoplasm 

 and yolk as possible. We have already seen that even the dissolution 

 of a number of the sister-cells of the ovum is sometimes demanded, so 

 that the ovum may be surrounded by nutritive follicular cells. In 

 short, the greatest possible quantity of nourishment is conveyed to the 



