FLEAS. 663 



are often taken for antennae (Fig. 416). The labium is thought by 

 some authorities to be represented by an unpaired median stylet, 

 but others regard this as a hypopharynx ; the labial palps are 

 semi-segmented and form two sheaths which enclose the piercing 

 organs. Ten pair of stigmata exist both in the larva and the 

 imago. The eggs are laid amongst the hair of the host but not 

 attached to them, so that they readily fall oft and the young 

 are reared amongst the dust under carpets and in like retreats. 

 The larvae (Fig.416) are something like miniature white wire-worms 

 (i.e. the larvae of Elaterid beetles), and they have a mandibulate 

 mouth. They eat all sorts of dusty refuse but can be reared on 

 moist bread crumbs. Before pupating they make a cocoon 

 often covered with dust. There are about a hundred described 

 species some of which seem confined to special hosts, but there is 

 much divergence of opinion as to how far one species of flea 

 migrates from one species of host to another. The rat flea 

 of India which conveys the plague from rat to rat undoubtedly 

 at times attacks man and is an active agent in infecting 

 man with the disease. It is not uncommon to find disused 

 houses swarming with fleas in such numbers that they can 

 almost be swept up with a broom, hence it seems clear that a 

 host, although desirable, may be absent at any rate for some 

 considerable period of the life-history. Two families are recog- 

 nized : 



Fam. 1. Pulicidae. The labial palps imperfectly divided into three 

 to five segments ; abdomen elongated and not greatly swollen in the 

 female with 

 ova. A c o s - 

 mopolitan family : 

 Pulex irritans is 

 the human flea, 

 P. avium infests 

 birds, P. serrati- 

 ceps dogs and 

 cats. The last 

 named species is 

 said to be an in- 

 termediate host Flo 41 7._ a Gravid female of Sarcopsylla penetrans. b foot of a 

 of the Cestode field mouse with a Sarcopsyllid attached (after H. Karsten). 



Dipylidium cani- 



num. There are many other genera. 



Fam. 2. Sarcopsyllidae. The labial palps have ten imperfect segments ; 

 abdomen short and in the fertilized female enormously swollen. This family 

 includes the Jigger or Chigoe flea, Sarcopsylla penetrans (Fig. 417), the 



