Studies on Chromosomes 



I 



89 



Both sexes with the same number of chromosomes; a pair of equal idiochro- 

 somes present in both. No visible difference between the two classes of sperma- 

 tozoa or between the male and female somatic groups. 



FERTILIZATION FORMULA 



Egg 'f + spermatozoon ^= zygote «(d' or 9) 

 Described Case 



To this type belongs also Oncopeltus fasciatus Dall, one of the Lygaeidae. It 

 is further probable that here belong many forms in which no visible sexual differ- 

 ences are to be seen, and in which idiochromosomes have not been identified. If a 

 particular pair of chromosomes, corresponding to idiochromosomes, are of general 

 occurrence, though not visibly distinguishable from the others, it is probable that 

 this type represents the most frequent condition in animals generally. 



II 



Both sexes, and both classes of spermatozoa, with the same number of chromo- 

 somes. The male with a pair of unequal idiochromosomes, half the spermatozoa 

 receiving the large one and half the small. In the female a pair of equal idiochromo- 

 somes like the large one of the male. 



FERTILIZATION FORMULA 



Egg 5 (including 7) + spermatozoon ^ (including ;') = zygote n (including /;') d" 

 Egg ^- (including/) + spermatozoon^ (including/) = zygote « (including //) 9 



