claim that the "determiners" may not be confined to the 

 chromosomes; and that certain enzymes or the known chemi- 

 cal specificity of the proteins and carbohydrates of the 

 cytoplasm may possibly function as carriers or determiners. 

 Moreover, no chemical differences can yet be detected be- 

 tween chromosomes carrying markedly different factors. 



Parthenogenesis. — Some animals and plants are able to 

 produce successive generations without fertilization of the 

 egg cell. This phenomenon is called parthenogenesis, and 

 is a common method of reproduction among plant-lice and 

 gall-wasps. It also occurs in the dandelion and the hawk- 

 weed. 



Parthenogenesis may be looked upon as a reversion by 

 the sexual producing animals and plants to an asexual power 

 possessed by their ancestors. 



In parthenogenetic individuals the chromosomes of the 

 egg are not reduced in maturation, consequently the off- 

 spring has the same number of chromosomes as the parent. 

 It is well known that in the case of bees, wasps and ants the 

 unfertilized eggs of the queen produce drones or males, and 

 the fertilized eggs, females. " In all known cases of parthen- 

 ogenesis the female is in the duplex condition and the male 

 is in the simplex, or partially duplex, condition. The fe- 

 male in all cases has the greater chromatin content." (Cas- 

 tle). 



Several experimenters have been able to cause the un- 

 fertilized egg to develop artificially by some physical change 

 or from the action of chemical substances, (page 141). 



(h)— The Control of Sex 



For ages breeders have looked for a method of con- 

 trolling sex. While recent studies seem to point to the 

 Mendelian character of sex, the predetermination of sex still 

 eludes the investigator. Many theories have been ad- 

 vanced but most have been discredited on rigid examina- 

 tion. 



The more important theories may be grouped as 

 follows : 



1. Those involving purely internal and organic factors: 

 (a) The predominance of one parent over the other 

 with reference to vigor and age. But opinions dif- 

 fer here as to the expected sex of the offspring. 

 Some cattle breeders maintain that the young bulls 

 beget a majority of males and the old bulls a ma- 

 jority of females. Some breeders believe that sex 



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