FLEAS 349 



material is in the fasces of the flea and transmission occurs by the licking on the part 

 of the rat of faeces from an infected flea. The infection has no connection with the 

 puncture wound of the flea as is the case with plague. As a result of the convincing 

 experiments of the Indian Plague Commission, their role in the transmission of 

 plague has been absolutely established. It is by the bite of the Xenopsylla cheopis 

 that plague is chiefly transmitted from rat to rat, and in bubonic and septicaemic 

 plague it is apparently the intermediary in human infection. 



The average capacity of a flea's stomach is about 0.5 cu. mm. so that with a rat 

 dying with septicaemic plague and with possibly 100,000,000 bacilli to i c.c. of 

 blood the flea would take in about 5000 bacilli. Furthermore these multiply in 

 the alimentary canal so that the digested blood teems with bacilli when reaching 

 the anus of the flea. The plague bacilli are passed out with the fasces and these 

 being rubbed into the puncture of the flea bite^ bring about infection. Regurgitation 

 as result of obstruction by masses of plague bacilli in the oesophagus causes in- 

 jection of plague bacilli into rat or man in the act of biting. This is more important 

 than the faeces inoculation method. The puncturing apparatus of the flea consists 

 of a pointed epipharynx and two distally serrated mandibles. These chitinous 

 biting parts are contained in the labium which divides distally into two labial palps. 

 The maxillae are conspicuous triangular structures and, projecting farthest anteriorly, 

 are the conspicuous four-jointed maxillary palps, often mistaken for antennae. 

 By the apposition of the internally grooved mandibles to the epipharynx a tube is 

 formed through which the blood is sucked up. The antennas are inconspicuous and 

 are in close apposition to the sides of the head, behind the eyes, and can only be 

 well made out with a lens. Fleas have three pairs of legs, and the male can be 

 distinguished from the female by its smaller size and the conspicuous coiled-up 

 penis within the abdomen. The female has a conspicuous gourd-like spermatheca 

 which varies in shape in different species. A very prominent structure is a pitted 

 plate in the ninth abdominal segment (pygidium). Of importance in classification 

 are prominent bristles originating from the seventh abdominal segments and 

 projecting over the pygidium. These bristles vary in number and are known 

 as antepygidial bristles. 



The body of the flea is flattened laterally. They may or may not have eyes, and 

 certain conspicuous structures called combs are of importance in classification. In 

 the metamorphosis of the flea the eggs are hatched out in dust of crevices, etc., into 

 bristled larvse in about one week. The larva forms a cocoon and develops into a 

 nymph which has three pairs of legs. The ftymphs emerge from the cocoon as adult 

 fleas in about three weeks after the larva forms it. 



KEY TO THE FLEAS 

 A. With combs, 

 i. Eyes present. 



(a) Combs along inferior border of head and on prothorax. 

 Ctenocephalus serraticeps. 



(b) Combs only on prothorax. Ceratophyllus fasciatus (with 

 only one antepygidial bristle on each side). 

 Hoplopsyllus anomalus (with many antepygidial bristles). 



