426 ENTOMOLOGICAL SOCIETY 



In Haematopinus there are some species, H. eurysternns and H. 

 vituli^ which have on the under side of the abdomen, near the end, 

 a pair of brush-like organs in the female, the precise function of 

 which it is somewhat difficult to understand, though it seems 

 probable that they are concerned in some manner with the re 

 productive function. 



There is often great disparity in the sexes, though, perhaps, no 

 more than is to be observed in many non-parasitic groups. In 

 Pediculidae the differences between males and females, either in 

 size or form, are not specially marked ; but in some of the genera 

 of Mallophaga, especially Lipeurus and Goniodes, the difference 

 is considerable, especially in the development of the antennas. 



In the mites the most striking difference between the sexes is, 

 perhaps, to be found in the genus Dermaleichus and its allies, 

 where the males are generally considerably larger and have poste 

 rior legs very greatly enlarged and apparently situated much 

 further back on the body than in the female. Modifications in 

 life-history are, in general, a tendency to the suppression of met 

 amorphoses, the extreme of this being reached in Hippoboscidas 

 and Nycteribiidae, but the same tendency is to be noticed in Pedi 

 culidae. Mallophaga, and the Arachnoids, the differences between 

 the larvae and adult being slight. 



When we come to my second category, the mode of life and the 

 character of the parasitism differ so decidedly from any of those 

 considered in the first category that it is difficult to discuss them 

 from the same standpoint. The parasitism in Hymenoptera is con 

 fined to the larva state, and since the larva in insects, as I have 

 repeatedly urged, undergoes an independent evolution, modified by 

 circumstances which affect this state alone, the influence upon 

 the adult is slight, and the modifications in the latter state are 

 hardly recognizable as due to parasitism. The adults are active, 

 highly organized insects, differing structurally to some extent from 

 allied groups of different habit, but hardly more so than from 

 each other. The distinctions between the four principal families, 

 Ichneumonidae, Braconidae, Chalcididae, and Proctotrypidaa, are 

 nearly as marked as between these families and their nearest 

 allies in the phytophagous (Cynipidae) and fossorial series. The 

 adults take but little food, and their chief modifications are in the 

 reproductive apparatus. The modifications are seldom striking, 



