72 



Fleas as a rule prefer certain hosts, but are not as particular in 

 this regard as are many parasites. Those species which are best 

 known are found to attack several hosts, including man. This 

 catholicity of taste is what makes them dangerous parasites, the 

 possible transmitters not only of plague, but also of consumption, 

 leprosy, etc. The fleas are treated by various writers under other 

 names, such as Aphaniptera, and Suctoria. About 300 species are 

 described, and perhaps as many more will be gathered by collectors. 

 Formerly all fleas were kept in the genus Pulex; now they are ar- 

 ranged in many genera, and these genera grouped into families. No 

 less than eight such families are recognized by some authorities on 

 this group. The species that occur on rats belong to three families, 

 which may be separated as follows : 



1. Thoracic segments much shortened and constricted; labial palpi apparently not 



jointed; third joint of antennae without sub joints; no ctenidia; abdomen of 



female becomes more or less swollen Sarcopsyllidse 



Thoracic segments not shortened nor constricted; labial palpi with joints; third 

 joint of antennae with several more or less distinct subjoints; ctenidia often 

 present; abdomen of female never distinctly swollen 2 



2. Posterior tibial spines in pairs Puliddse 



Posterior tibial spines mostly single and more numerous Ctenopsyllidse 



CTENOPSYLLID^E . 



To this family belongs the Ctenopsylla musculi Duges. 



This was formerly placed in the genus Typhlopsylla. The head 

 is rather acute in front and has four ctenidia each side; the eyes are 

 very small; the pronotal comb has 22 spines; each dorsal segment 

 of the body has two rows of hairs; the basal row of smaller hairs. 

 The proportions of joints in the hind tarsus are: 45-25-17-8-14. 

 Length 1.8 to 2.5 millimeters. This species is abundant on rats and 

 mice in Europe and other countries; recently it has been taken in 

 California and Florida on rats and mice. 



PULICID^E. 



This family includes the greater number of fleas. They have been 

 arranged in many genera, six of which have been taken from rats. 

 These are separable as follows: 



1. Head without ctenidia; eyes distinct 2 



Head and pronotum with ctenidia; last tarsal joint with four pairs of lateral 



spines 5 



2. Pronotum with ctenidia; female with one antepygidial bristle on each 



side Hoplopsyllus. 



Pronotum without ctenidia 3 



3. Last tarsal joint with four pairs of lateral spines; female with one antepygidial 



bristle each side 4 



Last tarsal joint with five pairs of lateral spines; female with two to five ante- 

 pygidial bristles each side Ceratophyllus. 



