552 MEDICAL ENTOMOLOGY 



difficult to distinguish from one another except by their size, but they 

 may be distinguished from the adults by the absence of the genital 

 apparatus which characterizes the sexes in the adult stage. In some 

 species of lice the number of prestomal teeth and the number of joints 

 in the antennae is greater in the adults than in the young, and localized 

 chitinizations of the integument, such as the sternal plates, are only 

 developed in the last instar. 



According to Warburton, who made a number of exact experiments 

 on the life history of the body louse, a further period of four days elapses 

 before the adults enter upon their sexual functions. The length of life 

 of the adult is given as at least three weeks in the male and a month in 

 the female, under artificial conditions, which, however, approached as 

 closely as possible to the normal. The first egg is laid soon after copu- 

 lation, and thereafter the female continues to oviposit at intervals during 

 the rest of her life, the large number of eggs laid serving to compensate 

 for the great susceptibility of the species to adverse conditions. Warbur- 

 ton found in one experiment that 124 eggs were laid in twenty-five days. 

 The time occupied in the growth from egg to adult is apparently 

 dependent on the supply of food rather than on the air temperature. 

 Warburton gives the following details of his experiment, carried out in 

 England in December. The larvae were fed at least twice in each 

 twenty-four hours. 



Incubation period .... eight days to five weeks. 



From larva to imago . . . eleven days. 



Non-functional mature condition . four days. 



Adult life >' male, three weeks. 



' ( female, four weeks. 



In an experiment carried out by the authors, in Madras in March, 

 with an average daily maximum temperature of 86 F., the following 

 results were obtained. The lice were fed only once in the twenty-four 

 hours. 



Larvae hatched on March llth and 12th, fed on . . 13th 



All moulted on 17th 



Second moult on 23rd 



Reached adult stage, final moult 29th 



The louse appears to spend most of its life clinging to the hairs or 



clothing of the host. Their powerful claws and stout muscular legs 



Habits enable them to take a very firm hold, and they are 



remarkably difficult to detach. They can, however, 



move very actively on occasion ; some of the species of Haematopinus 



