HEREDITY AND PROTOPLASM 



459 



chromosomes into two groups is called the reduction division, 

 since it reduces the number of chromosomes. 



In the formation of sperm cells also a reduction division 

 occurs. But instead of producing polar bodies the sperm 

 mother cell forms four sperm cells. 



The polar bodies formed by the maturing of the egg cell 

 die and disappear. 



When a sperm cell unites with an egg cell in fertilization, 

 the resulting zygote contains the full number of chromosomes, 



-\ 



/ 

 \ 



FIG. 245. The formation of an egg cell 



The chromatin material of the nucleus network, /, arranges itself into a definite number 

 of chromosomes, 2, which divide up into two equal groups, j. Half of the chromosomes 

 are pushed out of the cell, 4, and form the first polar body,/. The chromosomes of the 

 polar body, as well as the chromosomes remaining in the mother cell, split lengthwise, 

 and half of each chromosome is pushed out, 5. The first polar body thus becomes two 

 bodies, / x and / 2 , and the mother cell puts out a third polar body, / 3 , retaining half the 

 original number of chromosomes. This cell is now the egg cell 



half derived from the male parent and half from the female 

 parent. From all the evidence that is now available it would 

 seem that the chromosomes are the features of the germ cell 

 which bear whatever it is that determines the development of 

 the characters that distinguish the individual from otKers of the 

 same species, and at the same time those characters that 

 identify it with others of the same species. 



481. The germ plasm and acquired characters. According 

 to August Weismann (1834-1914) each organism is what it 

 is because it developed from a certain germ plasm. When 

 this organism produces new germ cells, it merely transmits 



