LIFE HISTORY OF P. VESTIMENTI 551 



is infected. It is a very hairy species, having two rows of long and 

 stout hairs on each of the abdominal segments dorsally, with longer hairs 

 at the sides, which cover up the pleural plates. The head is very short 

 and squat, the antennae being situated almost at its distal end. The 

 pleural plates are oblong, and the dorsal posterior angle of each is 

 produced into a short curved spine. The posterior border of each plate 

 bears two long hairs. The sternal plate is represented in figure 6. 



The subfamily Euhaematopininae of Enderlein contains only two 

 species, Haematopinoides squamosus, Osborn, and Eiihaematopinus 

 abnormis, Osborn. Both species are North American, the former from 

 Geomys bursanus, the latter from Scalops argentatus. 



The remaining genera do not contain any species of special interest. 

 Haematomyzus elephantis, the elephant louse, is distinguished from all 

 others by having the anterior part of the head drawn out to a tube-like 

 extension. 



LIFE HISTORY AND BIONOMICS 



Our knowledge of the life history and bionomics of lice rests princi- 

 pally on observations made on the species which infest man, and the 

 following account will accordingly refer particularly to Pediculus vesfi- 

 menti, the body louse. It is of course probable that the other species, 

 of a like habit and similar body structure, will have a similar life 

 history. 



The life history of the body louse (Plate LXIX) comprises a period 

 of gradual growth from the larva as it emerges from the egg to the 

 adult or reproductive stage. The period of growth 



is accompanied by several moults, in which the exo- 



r _ P. vestimenti 



skeleton is cast, but metamorphosis can hardly be 

 said to take place, since the young resemble the adults very closely. 

 The eggs (fig. 2) are small oval bodies of a dirty white or slightly yellowish 

 colour, pointed at one end and truncated at the end through which 

 the larva emerges ; they are just visible to the naked eye, and are 

 laid on the clothing and hairs of the host, being held in position by 

 means of a sticky substance excreted by the female at the time of 

 oviposition. Only one egg is laid at a time and in each place, though 

 oviposition takes place at frequent intervals. The young larva is 

 able to feed immediately it emerges, although it does not die if kept 

 without food for as long as two days ; thereafter it will feed, under arti- 

 ficial conditions, twice a day, and attains its full size in about eleven 

 days, after passing through three moults. The three immature forms are 



