226 Annals Entomological Society of America [Vol. XI, 



It has seemed advisable in this study to make drawings of 

 at least one thoracic segment of a member of each available 

 family of the Hemiptera. It is not necessary to present all of 

 these, for many families resemble each other closely in the 

 thoracic structure and separate drawings of these would be 

 largely repetitions. One or two families, on the other hand, are 

 omitted owing to an unfortunate lack of suitable specimens for 

 study. The observations on the Psyllidae as well as Figures 10 

 and 11 have been derived from the excellent monograph of 

 Crawford, 1914, on that family, the present writer having been 

 unable to secure specimens for study. Only drawings of such 

 forms as show marked deviation from the simpler type, and of 

 such individuals as offer features of particular interest are 

 presented. 



A slight attempt has been made at the end of the paper to 

 group those families which from their thoracic sclerites appear 

 to be more closely related. The grouping is made without 

 regard to other morphological features and thus may not be 

 entirely correct. It is hoped, however, that it may suggest, in 

 combination with other morphological characters, some idea of 

 the evolutional development of the Hemiptera. 



Having studied only a limited number of species representing 

 a family, the writer does not care to state that the characters of 

 these species obtain throughout the family. For convenience, 

 however, family names have been largely used in this paper 

 where specific names would have been more correct, it being 

 understood that, so used, they imply only those species studied 

 by the writer. Nevertheless, there is apparently not much 

 variation in a family, and one species may be considered as 

 more or less typical of the entire family. 



LIST OF FORMS STUDIED. 



In the preparation of this paper the following families and 

 their representatives were studied. The writer has not attempted 

 to arrange these in any logical order, but has followed the 

 sequence of families in Comstock's "Manual" for the Homop- 

 tera and that of Banks' "Catalogue of the Nearctic Hemiptera- 

 Heteroptera" for the Heteroptera. 



