294 



THE BIOLOGY OF INSECTS 



This wonderful and beautiful " wheel-foot " is character- 

 istic of the allied Trochopus (Fig. 74, c, d), whose species, 

 wingless and marine, skim over the surface of tropical 

 American seas not far from land. They are covered with 

 dense velvety hairs, and as a result carry down with them an 

 air-bubble when they dive ; this adaptation, common to a 



Fig. 74. — J, Veliid Marine Bug {Trochopus plumbeus), Jamaica, 

 X 10. b, fore foot with anchoring claws; c, intermediate foot with 

 " wheel" of feathered bristles, X 45; d, portion of "wheel," X 150. 

 After G. H. Carpenter {Ent. Mo. Mag. 1898). 



large number of aquatic insects, must be of especial value 

 to those that venture on the surface of the sea. 



The true pond-skaters (Gerris) with their elongate 

 slender legs are, as we have seen, among the most specialised 

 of freshwater insects that live on the surface-film. Members 

 of a related genus, Metrocoris, with several species on the 



