458 MEDICAL ENTOMOLOGY 



oblique. Both genal and pronotal combs are present. On the hind 

 edge of the tibia there is a close set row of bristles resembling a comb. 



One species, C. musculi, is a common flea of rats and mice, and has 

 become cosmopolitan in consequence. It is distinguished by having four 

 spines in the genal comb, and two bristles near the front angle of the 

 head which resemble the spines of the comb. 



GENUS HYSTRICHOPSYLLA, TASCHENBERG 



This genus is also very distinct, and has been placed in a separate 

 family, Hystrichopsyllidae, by Tiraboschi. The abdominal tergites, as 

 well as the genae and the pronotum, may bear combs. The number 

 of spines in the pronotal comb may be very large, and the integument as 

 a whole is very hairy. One species, H. tripectinata, occurs on rats 

 and mice in the Mediterranean. In this the genal comb is limited to the 

 lower edge of the gena, the first abdominal tergite only bears a comb, and 

 the remaining tergites have some small spines. 



Fleas pass through a complete metamorphosis comparable with that of 

 Diptera, from egg, larva and pupa to imago. Each stage resembles the 

 corresponding one in the Diptera. The life history of only a few species 

 has been followed out, and little or nothing is known regarding the varia- 

 tions which may exist in the different genera. Most of the observations 

 have been made on those fleas which are connected with rats and plague. 



The following applies to Ctenocephalus felis, which is com- 

 paratively easy to rear in the laboratory and to observe in its natural 

 habitat. The eggs (Plate LVII, fig. 16) are minute 



Metamorphosis: Life oya j bodies of a pearly white colour, just visible to 

 history of Ctenoce- , , , . , , . 



phaius felis tne na ^ed eye. They are deposited by the flea in 



places where the host is in the habit of sleeping, either 

 by day or by night, and are not attached to the surroundings in any 

 way, but simply dropped on the ground or bedding near the host. 

 About a dozen or a little more, judging from the examination of the 

 ovaries of apparently mature females, are laid at one time. It is not 

 often that the flea will lay all its eggs in a tube, where the}' may be 

 counted. The number which may be deposited by the fleas of a single 

 host in a night is enormous. One of the writers once saw the inside of 

 a hat, in which a kitten had spent the night, so covered with them that 

 it looked as if it had been sprinkled with sugar by a sifter. The eggs 

 hatch in from two to four days, according to. the temperature. 



