124 ENTOMOLOGY. 



mony between the different kinds and their surroundings, 

 and thus the order is rich in species and individuals. 



Darwin says that the sexes of Diptera differ little in 

 color; the greatest difference being in some species of Bibio, 

 in which the males are blackish or quite black, and the 

 females obscure brownish orange. In Elaphomyia of New 

 Guinea the males are homed. 



Dr. Williston writes us, however, that there are, upon 

 the whole, more sexual differences, aside from those in the 

 genitalia, among the Diptera than in any other order. In 

 the majority of species one finds but little difficulty in 

 distinguishing the sexes by secondary characters. In a 

 large proportion, also, there are minor colorational differ- 

 ences. Secondary sexual characters occur with extreme 

 rarity in the female, and in the male are chiefly confined to 

 the head and legs. 



Siib-order 1. Pupipara. — These are mostly wingless, de- 

 graded forms, which are born as pupa? from the body of the 

 parent, the egg and larval state having been passed within 

 the oviduct. The wingless species are remarkably spider- 

 like, the names bat-ticks and bird-ticks implying a resem- 

 blance to the ticks. 



Family Braulina.— Wingless, eyeless, minute insects with a large 

 head. The Bee-louse, Braula cteai Nitzseh. 



Fig. 143.— Bee-louse; a, its puparium. 



Family Nycteribidae. — The bat-ticks are spider-like, eyeless, or 

 with four ocelli; with a small head. They live on the fruit-bats. 

 Nycteribia westwoodii Guerin (Fig. 144). None exceed two lines in 

 length. 



