OF WASHINGTON. 



189 



from which the group is branched, one line becoming more 

 aquatic and reaching the extreme of specialization in this direc 

 tion, in such groups as Nepidas, Notonectidae, and Corisidae, the 

 other branch furnishing the terrestrial and arboreal families, while 

 they seem a generalized offshoot. We have further the carniv 

 orous division Reduviidae, which presents extreme branches in 

 Nabidas and Emesidae. 



As already mentioned, the Pediculidae may be considered a 

 retrograde branch connected with this portion of the Heteropter- 

 ous stem. These relations mav be exhibited as follows : 



While not expressing details in relation of sub-groups, this 

 sketch will call attention to the characters and plan which seem to 

 me must be recognized in arriving at a correct expression of rela 

 tionship. So far as catalogues or linear arrangements are neces 

 sary, the present system may be retained without great change, as 

 no linear arrangement can express correctly the relations stated. 



In the discussion Dr. Gill said that he considered the Homop- 

 tera to be the forms from which the Heteroptera were derived. 

 The aquatic forms were evidently derived from the terrestrial, 

 and should not be placed in a group by themselves, but should be 

 distributed among the families of terrestrial Hemiptera, with 

 which they are severally the most closely related. Mr. Schwarz 

 fully agreed with the speaker to the latter proposition, and 

 instanced the absurdity of placing all of the aquatic Coleoptera 



