( cxlv ) 



ences in the host of hosts, but must, at least in the main, 

 be attributed to those factors, whatever they may be, which 

 are the cause of the modification into geographical races of 

 non-parasitic insects and other members of the animal world. 



Epizoic life is, on the whole, one of ease and affluence, 

 attended by the results which we are wont to denominate 

 as degeneration. The females of certain sluggish or sedentary 

 fleas, such as species of Vermipsylla and the renowned Jigger, 

 Dermatophilus penetrans, swell up to a great extent, resem- 

 bling big lice or ticks in shape, the resemblance being enhanced 

 by their sluggish habits. A reduction in the mouth-parts of 

 Epizoa is of common occurrence. The palpi are absent in 

 the Anoplura or true Lice, and reduced in the Mallophaga, or 

 biting Lice, and the labial palpi of the fleas, which form the 

 outer sheath of the proboscis in this order of insects, are very 

 much reduced in those species which anchor themselves to 

 their host and thus lead a stationary life. 



While some Ectoparasites, like the Hippoboscidae and 

 Streblidae, have well-developed wings and have retained the 

 power of flight, these organs are entirely lost in other Epizoic 

 insects. We find remnants of wings or of wing-cases in the 

 Cimicidae, Polyctenidae, and Platypsyllidae and modified 

 halteres in the Nycteribiidae, but in the Hemimeridae, Sipho- 

 naptera, Mallophaga and Anoplura all remnants of wings are 

 lost. This convergent development is easy to understand in 

 Epizoa. Wings would be a hindrance and a danger to insects 

 moving among fur or feathers. For that reason, the winged 

 Pupipara break off the wings, or, at any rate, lose them 

 when they select their host, and in this state they resemble 

 more a bed-bug than a fly, which resemblance is, of course, 

 quite incidental, due to convergence without mimetic meaning. 



One of the most remarkable reductions among Epizoa is 

 that of the eyes. Epizoic species are derived from insects 

 with compound eyes. The facetted eye, however, is preserved 

 only in the Cimicidae and Hippoboscidae. In the Mallo- 

 phaga and Anoplura the eyes are reduced or absent ; in the 

 Nycteribiidae absent or vestigial; in the Polyctenidae, Hemi- 

 meridae and Platypsyllidae absent ; in Siphonaptera the eye is 

 single, never facetted, and in most cases reduced or absent. 



PROC. ENT. SOC. LOND., V. 1916. K 



