( clii ) 



body though the legs may be injured, or the body is provided 

 with strongly chitinised projecting lateral excrescences, as, for 

 instance, in the genus Hectopsylla (Siphonaptera), or with 

 specially thickened pleural sclerites as in certain Mallophaga. 



The non-stationary Epizoa have, instead, the advantage of 

 being able to run away, and they usually manage to find a 

 place on the body of the host where claw, tooth or beak cannot 

 well reach them. The majority of Epizoic insects have ac- 

 quired great agility, and many of them glide through the fur 

 of the host as quickly as a seal travels through water or a 

 corncrake through grass. Such rapid locomotion is only 

 possible in consequence of special adaptations. 



The Epizoa are all flat, and only the females of certain 

 stationary species swell up to a considerable extent. The 

 fleas are compressed, i. e. flat from the side, while all the 

 other Epizoic insects are depressed, i. e. flat in a dorso-ventral 

 sense. The head is rounded or conical, and sometimes as 

 flat and thin as the blade of a knife. In Mallophaga, some 

 Fleas, Pupipara, and others, it is the whole anterior portion 

 of the head corresponding to the clypeus which is smoothly 

 rounded. Stationary fleas, however, like the rabbit-flea and 

 the Jigger, have the frons angulate. In the Polyctenidae the 

 upper lip is very much enlarged and semi-circular in shape, 

 forming the anterior portion of the head into a kind of shield 

 (text-fig. 7). This shield is horizontal and very much re- 

 sembles the clypeus of certain Mallophaga. Now, among the 

 Siphonaptera we also find species in which there is such a 

 shield, but here it is homologous with the clypeus and not 

 with the labrum, and is placed in a vertical direction. This 

 occurs in Stephanocircus and some allied genera. The head 

 of the Nycteribiidae has not this rounded shape and is not 

 carried in the usual manner, but tucked away in a groove 

 on the upper side of the thorax. 



Such stowing away of projecting organs is a common de- 

 vice. The proboscis of the Cimicidae and Polyctenidae lies 

 in a groove on the under side, and that of the Siphonaptera 

 in between the fore coxae. The antennae of fleas (text- 

 figs. 8-13), Pupipara and certain Mallophaga are tucked 

 away in a groove. The antennae are nearly always short, 

 and, in those cases where there are many segments, most of 



