4 THE FLEA [OH. 



gradually lost, as they became useless, when a 

 partially parasitic life was adopted. At one time 

 entomologists regarded fleas as wingless flies and 

 placed them in the order Diptera. Certain supposed 

 scaly plates on their bodies were regarded as the 

 atrophied relics of wings. It is, however, more than 

 doubtful whether this view is correct ; and all modern 

 entomologists who have given any special study to 

 fleas are agreed that they are sufficiently unlike any 

 other living insects to deserve a place in an order by 

 themselves. To this order the name Siphonaptera 

 has been given: which means that the insects com- 

 prised in it are provided with sucking mouths and 

 are destitute of wings. Another name for the order 

 is Aphaniptera, but this is gradually falling into 

 disuse. Linnaeus (1758) only mentions two species 

 of flea : the human flea which he appropriately named 

 Pulex irritcms, and the chigoe of hot countries which 

 he called Pulex penetrans, from the habit which the 

 female has of burrowing under the skin of her victims. 

 At the time of writing, about 460 species of flea have 

 been described and named; but some of the names 

 are doubtless synonymous, and the actual number of 

 separable species that have been discovered is some- 

 where about four hundred. The vast majority of 

 these have been described within the last few years, 

 which shows what can be done when attention is 

 turned to any neglected group of animals. There 



