138 SECRETS OF ANIMAL LIFE 



chromosomes, which probably bear respectively 

 paternal and maternal hereditary qualities. Accord- 

 ing to Professor Brachet and some other authorities 

 the sperm-cell is not important in connection with 

 the transmission of specific characters that is the 

 ovum's role, but, in addition to its chief function 

 as "an agent in division," it may be credited with 

 being the vehicle of minor personal features char- 

 acteristic of the male parent. This view is a blow 

 to proud fathers, but it is probably the exaggera- 

 tion of an element of truth into a falsity. (2) The 

 fertilization, as we have mentioned, restores the 

 normal quantity of chromatin and the normal 

 number of chromosomes. In some cases, especially 

 among insects, it has been proved that there are two 

 kinds of sperm-cells, one contingent with, and the 

 other contingent without a special sex-chromosome, 

 and that the sex of the offspring hangs on the 

 fertilization. Thus an even number of chromosomes 

 in the fertilized ovum may mean a female offspring, 

 while an odd number may mean a male. In other 

 cases, however, the sex of the offspring is determined 

 by the physiological character of the egg-cell, 

 quite irrespective of fertilization. Thus Professor 

 Oscar Riddle has shown in pigeons that the eggs with 

 less intense metabolism and greater storage capac- 

 ity develop into females. (3) The entrance of the 

 sperm-cell implies the advent of a minute body 

 called the centrosome, a mountain-moving mouse, 

 which divides into two, and plays an important part 

 in the subsequent division, acting, as it has been 



