Siplionaptera, 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 
92. Head and pronotum of (a) deg flea; (b) of cat flea; (e) 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 
