ONTOGENESIS 231 



Canestrini long ago suggested that the sex of 

 the individual was determined by the number of 

 spermatozoa that enter the ovum at the time of 

 fertilization. But as it is now well known that 

 only one spermatozoon enters to fertilize the 

 ovum, of course this theory fails. 



That conditions of fertilization do have some- 

 thing to do with sex determination is, however, 

 quite certain. Thus,^ in bees the spermatozoa 

 of the male are contained sometimes during the 

 several years of the life of the queen, in living 

 condition, hi a special receptacle made to receive 

 them, from which they can be liberated to fertil- 

 ize the eggs or not, at the will of the queen. 

 Ordinarily the eggs are fertilized and all give rise 

 to females, but unfertilized eggs all develop into 

 males. 



II. Theories increasing in validity with increasing 

 knowledge of cytological science: 



E. That the sex of the individual is in every case 

 predetermined in the ovum. 



This must not be construed to mean that one 

 ovary produces male eggs and the other female 

 eggs, though such a theory has been held and 

 taught. There is, however, no doubt but that 

 some organisms, especially insects, produce eggs, 

 some of which are male and some female in qual- 

 ity, having morphological differences by which 

 they may be recognized. 



F. That the sex of the offspring is determined by 

 the spermatozoa. In its original form this idea 

 had no scientific foundation, for it was supposed 

 that the spermatozoa from one testis gave rise to 

 male, those from the other to female offspring. 



It began, however, to have significance in a 

 quite different sense, as a result of recent scien- 

 tific investigation of the germinal cells and the 

 mechanism of fertilization. Thus investigations 



