80 LICE AND THEIR MENACE TO MAN 



feed. It does not withdraw its mouth parts, but 

 continues in this one position for about five days, 

 sucking blood intermittently, and keeping itself 

 continually gorged, while it defaecates in a dis- 

 gusting manner. It moults three times, and after 

 the first moult it moves occasionally for a short 

 distance, but continues to take very protracted 

 and generous meals. It now holds two hairs 

 instead of one, and hangs with its body suspended 

 between them. In moving it always retains a 

 hair in the grasp of the legs of one side until it 

 has established its grip on another by means of 

 those of the other side. This sidling movement, 

 and the ungainly shape of the creature, earned 

 it its popular name. The growth of this louse 

 occupies a little over a fortnight, and the adult 

 female lays an average of about two eggs a day 

 for about another fortnight, by which time it 

 appears to have completed its natural span of life. 

 The insect has therefore a lower fecundity than 

 the others, but its eggs are nearly twice as large 

 in proportion to the size of its body. 



An idea is very prevalent that the young crab- 

 louse burrows under the skin. This is not the 

 case ; the false impression is gained by its very 

 close adherence to the surface and the difficulty 

 of dislodging it with the fingers. 



The spread of the crab-louse is usually by its 

 passage in some form from one sex to the other 

 during coitus, but it may be picked up by other 

 means. It was thought that it was disseminated 



