142 JOURNAL, BOMBAY N ATURAL HISTORY SOCIETY, Vol. X. 



lasts about twelve days in summer, rather longer in winter, and then the 

 grub spins round itself a silken cocoon, like that of the silkworm, and enters 

 upon a state of rest. Within this cocoon the larva changes into an inactive 

 pupa. Under the larval skin profound changes are taking place, and the 

 organs of the flea itself become developed, the legs, head appendages, and so 

 on make their appearance, but each is wrapped in a separate case of skin. 

 This inactive pupal stage lasts from ten to sixteen days, or may even, in cold 

 climates, continue through the winter ; then the flea immerges from the pupa, 

 bursting through the pupal skin and, issuing from the cocoon, commences its 

 predatory life on warm-blooded animals. 



Thus the life-history occupies rather less than a month, more or less, accord- 

 ing to temperature and surroundings. If there is no dust about on which the 

 larva can feed, it dies. There is no need to insist here on the fact that 

 cleanliness is a powerful enemy to the flea.^ 



The number of species of flea occurring in Great Britain can be stated only 

 with some reserve, but at least fourteen have been accurately distinguished by 

 German authorities, though only two of these at the most are predatory on 

 man. The common flea, which occurs on man, is Pulex irritans ; this is almost 

 cosmopolitan, though it is doubtful if it occurs in Equatorial regions. Man 

 is, however, stated to be subject to occasional attacks from the flea, naturally 

 living on the blood of the dog and cat, and known as P. serraticeps. It 

 is uncertain whether this species actually bites man. Some authors, even at the 

 present day, refer to the dog's flea, as P. canis, to the cat's flea, as P.felis, &c,, 

 but Saschenberg (1880) has shown that the fleas infesting the dog, cat and 

 many wild carnivora in reality belong to one species. The two fleas, P. irritans 

 and P. serraticepSj are much of a size, measuring from 2 to 3 millimeters in 

 length ; the thorax of the human flea is, however, larger than that of the 

 carnivore's flea, and the latter derives its name from the presence of two rows 

 of stiff hairs or bristles — one round the head and the other on the thorax. 



Fowls, pigeons, ducks, and, with few exceptions (for the parrot and wood- 

 pecker have each their own particular flea), the parasite of all birds is a third 

 species, P. avium. It is slenderer and longer (3 to 3'5 mm.) than the two pre- 

 ceding species. It possesses the thoracic bristles of the carnivore's flea, but it 

 is without the head spines ; and further, the antennge, which are inconspicuous 

 in the two preceding species, are here large and projecting. 



A fourth species (P. goniocephalus), smaller than the dog's flea, but rather 

 like it, is found on the rabbit and hare. The squirrel, badger, and hedgehog 

 each has its own species. 



^ Even as early as 1687 Leuwenhock, who made such excellent and surprising use of the 

 earliest microscopes, had published some facts of the flea's history. 



Kirby and Spence tell us that Hungarian shepherds were in the habit of greasing their 

 clothes and their person with hog's lard, and thereby " rendering themselves disgusting even 

 to fleas," 



