Siphonaptera, or Fleas 



121 



as in the case of lice, (Warburton) and varying conditions of tempera- 

 ture and humidity have practically no effect on the percentage of 

 eggs which ultimately hatch. 



The same investigator found that the most favorable condition 

 for the larva is a low temperature, combined with a high degree of 

 humidity; and that the presence of rubbish in which the larva may 

 bury itself is essential to its successful development. When larvae 

 are placed in a bottle containing either wood-wool soiled by excre- 

 ment, or with feathers or filter paper covered with dried blood they 



/ pa/pt 



92. Head and pronotum of (a) dcg flea; (6) of cat flea; (c) of hen flea. After Rothschild. 

 (d) Nycteridiphilus (Ishnopsyllus) hexactenus. After Oudemans. 



will thrive readily and pupate. They seem to have no choice be- 

 tween dried blood and powdered rat feces for food, and also feed 

 readily on flea excrement. They possess the curious habit of always 

 devouring their molted skins. 



An important part of Strickland's experiments dealt with the 

 question of duration of the pupal stage under the influence of tempera- 

 ture and with the longevity and habits of the adult. In October, 

 he placed a batch of freshly formed cocoons in a small dish that was 

 kept near a white rat in a deep glass jar in the laboratory. Two 

 months later one small and feeble flea had emerged, but no more 

 until February, four months after the beginning of the experiment. 

 Eight cocoons were then dissected and seven more found to contain 

 the imago fully formed but in a resting state. The remainder of 



