STUDY OF CHROMOSOMES IN NOTONECTA 145 



equal in certain individuals of N, glauca than in others. In the 

 other species, these chromosomes are more unequal, and are 

 extremely so in N. indie a. 



3) The X chromosome of N. indica is a compound chromo- 

 some composed of larger and smaller parts. 



4) In N. undulata, indica and shooterii, there are 14 chromo- 

 somes in the first division and 13 in the second and 26 in the 

 diploid groups. In N. irrorata and glauca, there are 13 chromo- 

 somes in the first division and 12 in the second and 24 in the di- 

 ploid groups. In N. insulata, there are 14 or 13 in the first and 

 12 in the second. 



5) In all the species except N. indica, the chromosomes in the 

 first division are arranged in a ring with the small ones in or near 

 the center. In N. indica, two of the intermediate chromosomes 

 are somewhat within the ring. In all the species in the second 

 division, the chromosomes are arranged in a ring with XY in 

 the center. 



6) In N. undulata, indica and in the 14-groups of insulata, 

 there are two small ones in the center of the ring in the first di- 

 vision. In N. irrorata and glauca and in the 13-groups of insu- 

 lata, there is only one small one in the center. In N. shooterii, 

 there is one small one in the center and another between the cen- 

 ter and the periphery. In the 13-groups of N. insulata, the sec- 

 ond small one is often found attached to the macrochromosome. 



7) Large double chromosomes are characteristic of N. insulata, 

 glauca and indica. 



8) The differences in somatic characters in the different spe- 

 cies cannot be definitely correlated with the differences in chro- 

 mosome number or arrangement. However, the 14-chromo- 

 some species are the smaller species, while the 13-chromosome 

 species are the larger ones. 



JOURNAL OF MOKPHOLOGY, VOL. 27, NO. 1 



