ORDER SIPHONAPTERA (APHANIPTERA) : FLEAS 193 



abdomen. The curved receptaculum seniinis is a conspicuous 

 object in the female when the animal is mounted as a 

 transparent object. 



The eggs are large and are dropped by the female 

 casually (?>., are not attached to the residential host of the 

 parent). They fall to the ground and may be found in the 

 places where domestic animals sleep. In summer the eggs 

 hatch in two, three, or four days, but in winter the develop- 

 ment within the egg may be prolonged to nearly a fortnight. 



The larva (Fig. 75) is an active, footless maggot, of a 

 whitish colour, and is sparsely but regularly hairy. It is 

 composed of a head and 13 segments of nearly uniform 

 diameter, the last segment ending in a pair of hooks. The 

 head carries a pair of small antenna, a pair of stout 

 serrated jaws, and a pair of maxillae with jointed palps. 



nerve corcT 

 -ant. 



Fio. 75.— Larva of Bat-flea ^Cerate 



The larva eats the organic matter contained in the dust in 

 which it lives, and in summer is full grown within a fortnight, 

 though in winter growth is much delayed. When full grown 

 the larva spins a cocoon, in which it pupates. 



The cocoon is generally coated with adherent dust, and 

 the pupa inside it is a small humpbacked creature faintly 

 resembling the adult. The duration of the pupal stage 

 depends upon the temperature, the usual term in warm 

 weather being about a fortnight. 



Classification. — The number of species of fleas already 

 known is considerable. Mr C. F. Baker, in his incomplete 

 revision of the order, gives a list of 135 species, and expresses 

 the opinion that many hundreds of species will eventually be 

 found. Our only concern here is with the limited number that 

 have been found upon the rats and mice that frequent human 

 dwellings, and with those few that attack man. These 

 belong to two families, the Pulicidce and the Sarcopsyllidce. 



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