May. '06] ENTOMOLOGICAL NEWS. 147 



for a novice in entomology to readily identify our Libellulas 

 with a key based on wing markings. Again in many of the 

 Calopteryginse there is great uniformity in the parts concerned 

 in copulation but great diversity of wing markings. The 

 genera Rhinocypha and Calopteryx may serve as examples, and 

 in both it has been shown that the sexes are attracted to each 

 other by movements and displays of color. On the other 

 hand, the species of Sympetrum, which are, with a few excep- 

 tions, very uniformly colored and without wing markings, 

 have some diversity in the form of the abdominal appendages 

 of the male and great diversity in the accessory genitalia of 

 the male and the vulvar lamina of the female. These differ- 

 ences reach a maximum of development in the swift-flying 

 Somatochloras which are, with one or two exception, without 

 wing markings and with bodies uniformly colored, but which 

 show a remarkable diversity in the abdominal appendages of 

 the male and the vulvar lamina of the female. In the Agrion- 

 ines and Lestes, species generally with colorless wings and weak 

 flight, there is great diversity in the structure of the male ap- 

 pendages and the female thorax. Upon these parts to a great 

 extent all authors have based the most satisfactory definitions 

 of species. That there is a fundamental difference in the 

 factors which contribute to or determine the preservation of 

 species, and that among certain species this factor is 

 the complexity of the sexual act, and among others it 

 is the possession of obvious external characters, deter- 

 mined possibly by sexual selection, is suggested by a com- 

 parison of Dr. Calvert's treatment of the genus Argia 

 (Agrioninse) in the Biologia Ceritrali- Americana, and DeSely's 

 treatment of Rhinocypha (Calopteryginse) in the Synopsis des 

 Caloptc7ygines and its Additions. In the Agrionine genus 

 Enallagma there is considerable uniformity in the size of species. 

 The species of the genus Lestes vary more in this particular. 

 It is in the Agrionines possibly that the most diverse forms 

 of abdominal appendages are found, though the Gomphines 

 (almost uniformly colorless-winged species) have these parts 

 developed in extremely different manners. The Aeschnines, 

 most of which have colorless wings, have considerable diver- 



