80 MAN, THE ANIMAL 



it is possible to bring about such results. It is 

 necessary to keep in mind the fact that the chro- 

 matin increases in amount during these changes 

 through a natural growth process. After elimina- 

 tion of chromatin, the egg is now ready to be fer- 

 tilized. It has been prepared for this important 

 event. 



The sperm in a similar manner passes through 

 special growth stages which result in a similar re- 

 duction in the chromatin. There is this important 

 distinction between the changes which take place 

 in the egg and those which occur in connection with 

 the sperm: instead of there remaining a single 

 egg and three abortive or diminutive eggs, the 

 "polar cells" of the diagram, there are four active 

 sperm cells, each of which is capable of fertilizing 

 an egg cell. When the division in the growing 

 sperm cell takes place, resulting in separating the 

 chromosomes into different sperm cells. Fig. 29, 

 there are produced sperms with a different chro- 

 matin content. This enables one to state then that 

 the sperms of a given generation are not all com- 

 posed of exactly the same kind of chromatin. The 

 several changes just briefly given in the egg and 

 sperm are limited to the nucleus. (Fig. 25.) 



The fundamental facts in connection with the 

 preparation for reproduction in the egg and sperm 

 are of the utmost importance. Around these facts 

 center the whole of our present-day interpretation 

 of heredity and sex. 



