REPRODUCTION 37 



of the egg nucleus. During their formation, the number 

 of chromosomes characteristic of the species is reduced 

 by half, so that when the egg nucleus is finally ready for 

 union with the sperm nucleus, it contains exactly one-half 

 the number of chromosomes usually present in the cell. 

 There are formed in all three polar bodies. The divisions 

 which occur in their formation separate the mass of 

 chromatin originally present in the germinal vesicle 

 into four equal parts. One-fourth part enters the egg 

 nucleus and the other three parts are distributed, one to 

 each of the polar bodies. The polar bodies are in no 

 direct way concerned in fertilization and soon disinte- 

 grate and disappear. 



37. Changes in the spermatozoon. After contact 

 with the egg, the tail of the sperm soon degenerates 

 either outside or, in some cases, inside the egg. 



The nucleus of the sperm grows rapidly in size. The 

 nucleus is further stimulated to cell division by the 

 influence of the cytoplasm of the egg. 



38. The significance of reduction. All the phenom- 

 ena attending the processes of fertilization seem to 

 have been specifically arranged for the purpose of bringing 

 about a reduction of the number of chromosomes in the 

 germ-cells to one-half that found in the other cells of the 

 body. A result so universal in plants and animals must 

 possess some significance in the reproduction of living 

 forms. This change is characteristic of the germ-cells 

 only and always occurs prior to and in preparation for 

 the union of the spermatozoon and the egg. What is 

 the real significance of the reduction of the chromosomes ? 

 Is this reduction of the chromatin a quantitative one, or 

 is it in some way a qualitative division? It must be 

 admitted that we cannot yet give positive answers to 



