504 Alice M. Boring 



Montgomery has for many years endeavored to determine the 

 stage of evolution by the number of chromosomes that a species 

 possesses, those having few being considered higher in the scale 

 than those with many. The chromatin nucleoli were supposed to 

 be degenerating chromosomes as a species evolves to a higher form. 

 But he has recently collected data from all the scattered literature, 

 tabulated the number of chromosomes and the species, and finds 

 that there is no such correlation ('06b). In the Hemiptera Homop- 

 tera there is no reason for considering Vanduzea arcuata, with 9 

 chromosomes, more highly evolved than Entilia sinuata, with 11, 

 or Phlepsius irrotatus, with 8, more so than Poeciloptera septen- 

 trionalis, with 14. 



Sex Determination 



We have seen in the historical review of the work on tracheate 

 spermatogenesis, that the most recent and reliable work all points 

 to a dimorphism of the spermatozoa in the forms with an odd chro- 

 mosome or an unequal pair of chromosomes. McClung was the 

 first to suggest that the one characteristic that most generally 

 divides the animal kingdom into two equal classes is sex, and that 

 therefore, the dimorphism of sex and of spermatozoa may be 

 causally connected. There is need of careful statistical work on 

 the proportion of males and females among different species of 

 insects. In general collecting, however, one gets an impression of 

 equality in numbers. McClung's theory was a brilliant guess, 

 which the work of Stevens and Wilson has substantiated. 



The Hemiptera Homoptera furnish additional evidence for this 

 theory. Females of many of the species were sectioned for oogo- 

 nial and somatic equatorial plates. Only two furnished the desired 

 stages, Poeciloptera septentrionalis and Poeciloptera pruinosa. 

 In both the spermatogonial number is 27, the spermatozoa pos- 

 sessing 13 and 14 chromosomes, and the female somatic number is 

 28. Stevens and Wilson have shown that there is no difi^erence 

 between the somatic number and the unreduced number in the 

 germ cells; in the female, both numbers are even, in the male, 

 both are odd (or even, when a small chromosome is included). 

 As the female somatic number in Poeciloptera is even, the oogonial 



