( cxlviii ) 



degree of parasitism is of less importance in connection with 

 the reduction of the eye than the absence of light, in the 

 imagines of Epizoic insects. The absence of light leads to 

 the reduction of the eyes, whether the insects are parasitic 

 or not. Our illustrations (text-figs. 8-13) represent two 

 series of three fleas each, showing a gradual reduction of the 

 eye in closely related species. 



The reduction or loss of the power of flight and of the eye- 

 sight are clearly cases coming under the term of loss of organs 

 by disuse. But not every instance of reduction of organs 

 among Epizoa is attributable to the same cause. In the 

 Mallophaga, for instance, the foreleg is often much shortened, 

 being modified into a sort of hand employed while feeding 

 (text-fig. 14). In a similar way, the forelegs of Polyctenidae , 



Fig. 14. Underside of head and prothorax of Esthiopterum diomedeae 

 Fabr. (1775). 

 ,, 15. Underside of head and prothorax of Eoctenes nycteridis Horv. 

 (1910). 



widely removed from the Mallophaga in classification, are so 

 short that they are entirely concealed under the prothorax. 

 They are strongly built, particularly the femora, and certainly 

 not without functions (text-fig. 15). It is possible that the 

 Polyctenids use them while feeding for keeping the- hairs of 

 the host away from the proboscis. This convergent develop- 

 ment between Mallophaga with biting mouth-parts, living on 

 birds and mammals, and Polyctenids with sucking mouth- 



