246 INSECTA. 



are broad and compressed, so as to present an extensive surface to 

 the water, which is still further enlarged by the presence of flat spines 

 appended to the end of the tibia, as well as of a broad fringe of 

 stiff hairs inserted all around the tarsus. The powerful oars thus 

 formed can open until they form right angles with the axis of the 

 body, and from the strength of their stroke are well adapted to the 

 piratical habits of their possessors, who wage successful war not 

 only with other aquatic insects and worms, but even with small 

 fishes, the co-inhabitants of the ponds wherein they live. 



The same principles are carried out even more perfectly in the 

 construction of the swimming legs of the water-boatman (Noto- 

 necta), a kind of water-bug. The resemblance of this creature 

 (Jig. 101, G, H) to a boat with its oars, cannot escape the most in- 

 attentive examiner ; and the similarity is still further increased by 

 its manner of swimming ; for, as it preys, upon insects that have 

 been accidentally drowned by falling into the water, it usually rows 

 itself about upon its back, because in such a position it can best 

 watch for its victims. 



(287.) The wings of insects, when present, are invariably attached 

 to the two posterior segments of the thorax, which, as we have al- 

 ready seen, are strengthened in every possible manner, so as to afford 

 a support of sufficient density and firmness to sustain the violent ex- 

 ertions of the muscles inserted into the organs of flight. 



In the most perfectly organized families the wings are four 

 in number, as in the Neuroptera (Jig. 103), the Hymenoptera 

 (Jig. 129), the Orthoptera (Jig. 102), the Dictyoptera, the He- 

 miptera (Jig. 101), the Lepidoptera (Jig. 105), and the Cole- 

 optera (Jig. 106). 



In the Dipterous insects there are only two wings, which are 

 fixed upon the central segment of the thorax ; while, in the posi- 

 tion usually occupied by the posterior pair, we find a pair of pe- 

 dunculated globular bodies, usually named the Halteres or poisers, 

 as in the gnat (Culex,) (Jig. 131, F). 



But, in every one of the orders above enumerated, there are 

 certain families which, throughout the whole period of their exist- 

 ence, are never provided with wings at all ; and these by many 

 entomologists have been formed into an order by themselves, under 

 the name of Apterous insects. In the opinion of Burmeister,* 

 whose classification we have adopted, such an arrangement is 

 purely artificial, inasmuch as it must embrace insects of most 



* Manual of Entom. p. 623. 



