42 THE FIRST PRINCIPLES OF HEREDITY 



cell takes place earlier, during the process of its formation 

 — i.e., during spermatogenesis. Furthermore, while the 

 products of the reducing division of the ovum are, as we 

 have seen, of unequal size, the three small polar bodies 

 being cast away, in spermatogenesis all the resulting cells 

 are of equal size, and capable of functioning. Otherwise 

 the two processes are in every respect alike. We have a 

 sperm-cell with, let us say, four chromosomes again. As 

 this cell grows, it doubles its number of chromosomes to 

 eight. Then this mother sperm-cell goes through a double 

 reducing division, first splitting up into two daughter- cells 

 with four chromosomes each, and finally into four grand- 

 daughter sperm-cells with two chromosomes each. These 

 are all of equal size, and all function as sperm-cells. They 

 are the primitive spermatozoa, which soon assume the 

 proper shape characteristic for each species. 



The parallelism will be made quite clear in the adjoined 

 scheme (Fig. 30). 



We must add that in both cases the chromosomes 

 finally lose their identity, forming a network of chromatin, 

 as shown in the ordinary body-cells. 



I V.—FERTILIZA TION. 



It is a strange fact that, although the union of both sexes 

 was thought to be the essential factor in the act of repro- 

 duction (see Chapter II.), it was a considerable time before 

 the true import of both male and female germs was 

 recognized. Two schools — the Ovists and Animalculists — 

 held sway for a long time in fierce opposition to each other, 

 the former declaring the ovum as the aU-important element 

 in fertilization, while the other attributed this role, with 

 the same one-sidedness, to the spermatozoon (animalcule). 

 And even after due credit had been given to both elements 

 alike, the real meaning of their union was far from being 

 understood, it being held that a sort of seminal breath 

 (aura seminalis) passed from the seminal fluid to the 



