VII FLEAS 525 



the apartment. The cat -flea can pass through its growth and 

 metamorphosis with excessive rapidity, the entire development of 

 a generation in favourable conditions extending but little beyond 

 a fortnight.^ 



About a hundred kinds of fleas are known, all of which live 

 on mammals or birds, Hystriclio'psylla tal'pae (Fig. 250) is one 

 of the largest, it occurs on the Mole. It was found by Eitsema 

 in the nests of Bomhus suhterraneus (and was described under 

 the name of Pulex ohtusiceps). As these nests are known to be 

 harried by Voles, and as this flea has also been found on Field- 

 mice, it is probable that the parasites are carried to the nests 

 by the Voles. The species that chiefly infests man is Pulex 

 irritans, an Insect that is nearly cosmopolitan, though arid desert 

 regions are apparently unsuitable to it. Pulex avium occurs on 

 a great variety of birds. P. serraticeiis infests the dog and the 

 catj as well as a variety of other Mammals. It is a common 

 opinion that each species of Mammal has its own peculiar flea, 

 but this is far from correct. Fleas pass readily from one species 

 of animal to another ; the writer formerly possessed a cat that 

 was a most determined and successful hunter of rabbits, and she 

 frequently returned from her excursions swarming with fleas that 

 she had become infested with when in the rabbits' burrows ; her 

 ears were on some occasions very sore from the flea-bites. Some 

 of the fleas of other animals undoubtedly bite man. There 

 appears, however, to be much difference in the liability of different 

 individuals of our own species to the bites of fleas. Sarcopsylla 

 Ipenetrans differs in habits from other fleas, as the female 

 buries the anterior parts of her body in the flesh of man or 

 other Vertebrates, and the abdomen then becomes enormously 

 enlarged and distended and undergoes a series of changes that 

 are of much interest." "While in this position the Insect dis- 

 charges a number of eggs. This species multiplies sufficiently 

 to become a serious pest in certain regions, the body of one man 

 having been known to be affording hospitality to 300 of these 

 fleas. Sarcopsylla penetrans is known as the Sand -flea, or 

 chigger, and by numerous other names. Originally a native of 

 tropical America it has been carried to other parts of the world. 

 Another Sarcopsylla, S. gaUinacea, attaches itself to the eyelids 



1 Howard, Bull. Dcp. Agric. Ent. IST.S. No. 4, 1896. 

 - Schimkewitsch, Zool. Anz. vii. 1884, p. 673. 



