v] HUMAN FLEA AND OTHER SPECIES 65 



well-established and thriving parasite. Unfortunately, 

 there is no means of knowing whether this was the 

 case among the native populations before European 

 travellers and traders arrived. Pulex irritans has, 

 however, recently been found on the natives of 

 German New Guinea living some 10,000 feet above 

 sea-level and in great isolation. Seaports are every- 

 where infested with fleas. 



Another problem on which no light has been 

 thrown concerns the evolution of the human flea. 

 It would be of great interest to know whether the 

 present species has undergone modifications of form 

 since it became a parasite of the human race ; whether 

 we inherited the species from our simian ancestors; 

 or whether the flea of one of the lower mammals 

 became parasitic on mankind. In the Old World 

 this flea is essentially a parasite of man. It occurs 

 only occasionally on other mammals. In America 

 it certainly appears to occur more frequently on 

 mammals, other than man, than it does in the Old 

 World. Human fleas can propagate in deserted 

 human dwellings. The larvae find nourishment in 

 any refuse that has been left behind, and the adult 

 insect can apparently continue for some time to 

 reproduce itself without a meal of any sort and 

 certainly without human blood. Travellers in the 

 East and in Africa have described how on entering 

 huts in deserted villages they have found their 



K. F. 5 



