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CHAPTER III. 
SIPHONAPTERA. 
Fleas. 
This group of insects, including the well-known fleas, has by many 
writers been considered as related to the Diptera, but in most recent 
works on systematic entomology it is given separate rank under the 
above name. It is unnecessary here to discuss the question of their 
zoological position, but it may not be out of place to remark that, while 
they are avery distinct group and doubtless well deserve to have this 
distinction indicated systematically, there is much to indicate that they 
have had a remote relationship to the dipterous branch. This is shown 
not only in-the mouth parts and feet of the adults, but in the larve, 
which are footless, slender, worm-like creatures. 
The insects of this group are characterized by the entire absence of 
wings, by having the bodies compressed, the legs long and stout, the 
Fic. 76.—Pulex irritans: a, larva; b, pupa; c, imago—all enlarged (from Van Beneden). 
cox being remarkably developed, giving them great leaping power. 
The mouth parts are well developed and adapted for suction, all the 
species in the adult stage feeding upon the blood of mammals or birds. 
The antenne are small, usually sunken in a pit or groove in the side of 
the head and of peculiar form, the third, or terminal, segment being 
annulated, or, in some cases, even divided into leaf-like plates. The 
eyes are simple when present, but in many cases they are reduced to 
mere rudiments or even completely wanting. The tarsi are 5-jointed. 
They undergo a complete metamorphosis, the early stages being 
passed in places adjacent to the resorts of the host. The eggs, while 
sometimes laid upon the hairs of the host animal, are loosely attached 
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