78 



Lice usually walk sideways, but do not travel much, and they keep 

 close to one host. The eggs are slightly elongate and fastened to 

 the hair of the host. They hatch in about ten to fifteen days, the 

 young coming out of the top of the egg. These young do not differ 

 much in structure from the adults, but are paler in color. They 

 molt their skin a few times, probably four, before they reach the 

 mature condition. The males are less numerous than the females, 

 and ordinarily smaller. There are several generations each year, 

 dependent doubtless on the temperature; but the life history is not 

 thoroughly known for any species. After sucking the blood the 

 abdomen of the louse becomes somewhat distended, very noticeably 

 so in some species. 



The sucking habits of the lice render them dangerous parasites 

 and capable of transmitting a disease from one host to another. For- 



FIG. 7. Louse (Polyplax spinulosus). 



tunately they do not readily change hosts so that they can not be 

 considered quite as dangerous as some more active parasites. How- 

 ever, several species have already been shown to carry diseases in 

 laboratory experiments. Therefore it is probable that some of them 

 will be connected with the origin and diffusion of certain diseases of 

 animals. 



The Anoplura, or lice, have often been treated in connection with 

 the Mallophaga, or biting lice. This is doubtless because they fre- 

 quently occur on the same animal, and have a general resemblance 

 to them. However, they have no real affinity to these insects, and the 

 general opinion is that they are more or less related to the Hemiptera. 

 Sometimes they are treated as a group or section of the Hemiptera, 

 but also as a separate order, under various names as Siphunculata, 

 Lipognatha, Pseudorhynchota, and Ellipoptera. 



There are about 50 or 60 known species which are arranged in 15 

 genera and 4 families. Four species belonging to three different 



