HUMAN PEDICULI 335 



cast their skin several times as they increase in size, 

 and ultimately mature their reproductive organs, but 

 no other change ensues. The young Pediculus be- 

 comes full-grown in about a month, and is active 

 throughout life, and ever ready for blood-sucking. Thus 

 man's three personal blood-sucking parasites exhibit 

 three distinct types of development, the flea, passing 

 through a complete metamorphosis larva, quiescent 

 pupa, and perfect insect ; the bug, an incomplete meta- 

 morphosis, having an active pupa stage, and acquiring 

 rudimentary wings ; the louse, no metamorphosis at all, 

 there being no resting stage, and not the faintest sem- 

 blance of wings ever appearing. 



Pediculi are extremely prolific creatures, producing 

 large numbers of eggs, and, as we have seen, passing 

 rapidly into the adult and procreative condition, so that 

 generation succeeds generation with undesirable speed 

 and detestable powers of multiplication. Exact experi- 

 ments as to the degree of fecundity they exhibit it is 

 obviously not easy to persuade any one to undertake; 

 nevertheless, some naturalists have so far conquered 

 their repugnance as to investigate the matter slightly. 

 There has long been a popular saying, evidently begotten 

 of despair at their excessive multiplication, that a louse 

 can become a grandfather in twenty-four hours. This, 

 as mentioned above, is a great exaggeration, and so 

 thought Leeuwenhoek, who nourished about 200 years 

 ago ; he decided, therefore, to undertake a series of 

 experiments in order to settle the point and to work out 

 the life-history, if possible. The species he experimented 

 upon would appear to have been P. vestimenti, the body- 

 louse, but the conclusions would probably have been 

 similar with either species. His first thought was to 

 hire some poor child whom he might use as a host, the 



