HEAD LOUSE 395 



habits, however, it differs very slightly from its relative. It is 

 commonly smaller in size, and is more distinctly festooned along 

 the sides, due to constrictions at the joints between the segments. 

 Nuttall, however, has shown that all of the supposed morpho- 

 logical and biological differences between these two kinds of lice 

 are inconstant, and they should, therefore, be considered as 

 races of a single species. The head louse assumes all the char- 

 acteristics of the body louse when reared under conditions suit- 

 able for the latter. 



The head louse although usually preferring the fine hair of the 

 head as a habitat occasionally wanders to other parts of the body 

 as well. It is found in every part of the world. Different vari- 

 eties are said to occur on the different human races and to vary 

 in color with the color of the skin on which they live. The 

 lice which live on the white race are pale gray with a dark line 

 along each side of the abdomen, those on negroes are blackish 

 or brown, on Hindoos smoky brown, on Japanese and Chinese 

 yellowish, and on American Indians dark reddish brown. What 

 a wonderful case of protective coloration, except that, as in so 

 many other cases of so-called protective coloration, there is no 

 practical protection. A negro is as likely to scratch out a black 

 louse as a white one! 



As in the case of the body louse reproduction is very rapid but 

 the egg production is lower, due to the smaller capacity of the 

 body, even taking into consideration the slightly smaller size 

 of the eggs. The course of development is practically the same 

 in both species. The average number of eggs, according to 

 Bacot's observations, is from 80 to 100. Only one mature egg 

 can be developed in the louse's body at a time, but the suc- 

 cession of them is so rapid that eight or ten may be laid in a 

 day. Each egg or " nit " is glued by the lower end to a hair 

 (Fig. 175 A), the favorite " nests " being the vicinity of the ears. 

 The young lice hatch in ten or 12 days and reach maturity in 

 two or three weeks, and are then ready to reproduce again. At 

 this rate of reproduction, allowing only a 50 per cent hatch, a 

 single pair of lice theoretically could produce over three-quarters 

 of a million offspring in the fourth generation, and in the course 

 of less than three months! 



Although the bites of this species are not quite so irritating as 

 are those of the body louse, yet the frequent piercing of the skin 

 for a gory meal results in much scratching. Often the bites 

 swell into pimples which may bleed when scratched or which 



