STUDY OF CHROMOSOMES OF LACHNOSTERNA. QI 



period as definite compact chromatic bodies. They are always 

 contained within a chromosomal vesicle such as has been de- 

 scribed by Wilson ('12) in Oncopeltus and Lygeeus (Figs. 21, 25). 

 In Lachnosterna the sex elements usually remain separate from 

 each other, each enclosed in a separate vesicle. In Pelidonota 

 and Cotalpa, the sex pair remain fused during the synaptic 

 period, the smaller (y) element usually being imbedded along the 

 side of the larger (x) element. 



E. GENERAL CONSIDERATIONS. 

 i. Chromosome Number and Species. 



The intensive work of McClung and his students on one family 

 of Orthoptera, the Acrididse, has shown that the chromosome 

 number in all the species studied of this group is the same, 

 namely 23 in the male. This has led McClung to the generali- 

 zation that species closely related taxonomically might show 

 similarity in their chromosome groups. It is very evident that 

 this generalization cannot apply to all groups since, in some 

 cases there is a wide divergence in chromosome number among 

 members of the same genus. It is possible that in some cases 

 this difference in chromosome number between closely related 

 species may be due to a fusion of several chromosomes or else a 

 breaking up of one or more chromosomes into several distinct 

 components. In the case of Hesperotettix, McClung ('17) has 

 shown that the chromosome number may vary from 17 to 23. 

 He has shown that these variations are due to a fusion of chromo- 

 somes resulting in the formation of "multiple chromosomes." 

 In one species, Hesperotettix viridis, he has found the haploid or 

 reduced number to vary from 9 to 13. On the other hand, the 

 work of Stevens on the Diabrolicas (Coleoptera) has shown that 

 the species vitatta has 21 chromosomes, while the species soror 

 and 12-punctata have but 19. However, in the latter two species 

 there may be present from i to 4 additional or "supernumary " 

 small chromosomes. It is quite possible that the supernumary 

 chromosomes of the species soror and 12-punctata represent the 

 fragments of a pair of chromosomes, which would therefore make 

 an agreement in chromosome number between these two species 

 and the species vitatta. As McClung ('17, p. 545) has pointed 



