i] INTRODUCTORY 19 



turned into fleas, probably Pulex irritans. These 

 fleas, being confined without other food, were observed 

 to prey on the Lepidopterous larvae and to feed freely 

 on their juices. The larvae which were attacked by 

 fleas pined and died. The fluid from the stomach 

 of the fleas when they were crushed was transparent 

 and not red like vertebrate blood which often exudes 

 when a mammalian flea is pinched and cracked 

 open. 



A French entomologist has also reported that 

 the numerous fleas which swarm in the dwelling- 

 houses of Corsica, for want of other nourishment 

 turn their attention to flies that may be incapable 

 of flight. 



The only fossil remains of a flea that have, so far, 

 been discovered are a single insect in a piece of Baltic 

 amber of Oligoceue age. Many organic remains have 

 been preserved in this fashion, but this is the first 

 mammalian parasite that has been found. The flea 

 is admirably protected by its semi-transparent sur- 

 roundings, and the most minute details of structure, 

 the arrangement of bristles on the body, and the 

 number of segments to the labial palpi can be dis- 

 cerned. This unique object is in the collection of 

 Professor Klebs. The first point to note is that a 

 flea of this antiquity hardly differs from the existing 

 insects of the present day. It has been referred to 

 an existing genus (Palceopsylld) of which there are 



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