CHAPTER XVI 



Order Anoplura, or Siphunculata (Blood-sucking Lice) 



The lice, which some authors regard as a suborder of the 

 Rhynchota, are small, flat, wingless, blood-suckiftg parasites 

 of mammals, clinging to the hairs of their host by their 

 powerful claws. There is no metamorphosis. 



Lice much resemble Mallophaga, but can at once be 

 distinguished from them, under the microscope, by the 

 absence of mandibles. The species that are parasitic on 

 man have been supposed, like the bed-bugs, to disseminate 

 various pathogenic microbes — e.g. of tubercle, leprosy, typhus 

 fever, plague, relapsing fever, etc. — and to pave the way for 

 various infections of the skin. The trypanosome {T. lewisi) of 

 the rat can undergo certain developmental stages in the 

 rat-louse (^Hceinatopinus spinulosus). 



The head of the louse is small, and the antennae, which 

 consist of 3, 4, or 5 segments, are stumpy ; the eyes, which 

 are simple, are set far back. The mouth-parts consist of two 

 tubes, one inside the other, both being completely retractile ; 

 the outer, ensheathing tube, which is supposed to be homo- 

 logous with the labium of other insects, has its free edge 

 armed with tiny booklets, and is used for attachment to the 

 skin of the host when the insect sucks ; the inner, ensheathed 

 tube, which is supposed to represent the united mandibles 

 and maxillae, is the sucking organ, and when in action is 

 insinuated deep into the skin of the host. These tubes can 

 only very rarely indeed be made out at all satisfactorily in 

 the dead insect ; in the specimen figured (Fig. 94) which was 

 immersed in creosote when in a state of repletion, both tubes 

 are just visible, being not completely retracted into the 



head. 



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