SOME WINGLESS INSECTS 157 



these are not seen in the immature louse during the four or 

 five stages through which it grows into the adult condition. 

 But if a louse late in the last stage but one be examined, these 

 characteristic structures of the adult can be detected in the 

 cuticle which beneath that in present use is being prepared 

 for the final moult. The wingless lice give us, therefore, an 

 example of an insect life-history in which growth is accom- 

 panied by the least degree of change a life-history without 

 transformation. And we realize that this condition is appro- 

 priate to creatures which pass their whole existence, from the 

 egg to the adult stage, in the curiously specialized and uniform 

 surroundings afforded by the bodies of their hosts. 



Besides these blood-sucking lice (Anoplura), specimens of 

 another order of parasitic wingless insects are to be found 

 clinging to the hairs of mammals ; these are " biting-lice ' 

 (Mallophaga, Fig. 90), though the great majority of them live 

 on the bodies of birds. They are superficially rather like the 

 Anoplura, but may be readily distinguished by their entirely 

 different mouth-parts ; for a mallophagan possesses, instead 

 of a suctorial tube, strong paired mandibles, rather like 

 those of a grasshopper, and the insects feed by biting or 

 nibbling at the feathers or hairs and skin of their hosts. In one 

 of the families the foot bears the two claws usual among insects 

 and these Mallophaga (which live on birds) may be able, if 

 their host die, to go in search of a fresh one. Here then is an 

 example of periods of parasitism alternating with intervals 

 of migration. But many biting-lice have a single-clawed foot 

 (Fig. 90 a) adapted for clinging, essentially similar to that of 

 a blood-sucking louse, and Mallophaga of this type spend the 

 whole of their lives from the egg to the adult state attached 

 to hair or feathers on the bodies of their hosts, and as the 

 newly-hatched young resemble closely their parents in all 

 essential features and in most points of structural detail, they 

 also afford an example of a group of parasitic insects, wingless 

 throughout life whose growth is unaccompanied by any 

 marked degree of change. 



These Mallophaga or biting-lice are now generally regarded 

 as a distinct order of insects, but few students doubt that 

 they show affinity to the Corrodentia (the book-lice and their 

 allies) and some classifiers of insects still prefer to regard the 



