STUDY OF CHROMOSOMES IN NOTONECTA 121 



Morgan and many others that even within certain genera, there 

 is a discrepancy in the number of chromosomes in tKe different 

 species entirely disproportional to the differences in body char- 

 acters; for example, different species of phylloxerans have 6, 8, 

 12, and 22 chromosomes (Morgan '09). So true is this in the 

 case of certain Homoptera, that Boring ('07), after a study of 

 twenty-two species, concluded that the number of chromosomes 

 is of no significance for grouping species into genera. On the 

 other hand, there are fortunately other groups which are quite 

 favorable for a solution of this problem. The orthopteran fam- 

 ily, Acrididae, has engaged the attention of McClung for some 

 time in an effort to discover the relation between chromosomes 

 and somatic characters. The forty genera already examined, 

 have, with a few exceptions, shown the same number of chro- 

 mosomes, and the constancy in number, size and form of the 

 chromosomes has led McClung ('05, '08, '14) to a belief in their 

 importance in taxonomy. A peculiar association of some of the 

 chromosomes in certain genera and species is believed by him 

 to be directly responsible for the generic or specific somatic 

 characters of those forms. The genus Notonecta, consisting as 

 it does of many species differing from each other slightly, but 

 characteristically, both in somatic characters and in chromosome 

 content, offers another very favorable object for the study of 

 this problem. 



II. SPECIES OF NOTONECTA 



The genus Notonecta includes, according to the entomologists, 

 Kirkaldy ('97) and Bueno ('05), twenty species, thirteen of which 

 are peculiar to America. One species (N. luteaj is common to 

 America, Europe and Asia; one (N. glauca) is common to Europe, 

 Asia and Africa; one (N. lactitans) is African; one (N. handlir- 

 schli) is Australian; and three (N. chinensis, N. montandoni, 

 N. triguttata) are Asiatic. My former paper (Browne '13) 

 dealt with three of the American forms common in the eastern 

 United States, N. undulata, N. irrorata, and N. insulata. 

 The present paper deals with the European N. glauca, and two 



