FORM, GROWTH, AND CHANGE 15 



hopper's hind thigh is necessary for the inclusion and attach- 

 ment of the great muscles which move the shin. 



The structure of the legs is of importance to the student of 

 insect transformations because these organs show varying 

 degrees of development in different insect-larvae both as 

 compared with one another and with the perfect insects into 

 which they grow. 



The second and third thoracic segments mesothorax and 

 metathorax are outstanding because to them are attached 

 the wings, those characteristic organs for effecting the insect's 

 motion through the air. An insect's wing 1 must be regarded 

 as a lateral outgrowth of the body, bounded by a thin extension 

 of skin covered outwardly by cuticle, the whole structure 

 flattened from above downwards so that the original cavity 

 becomes to a great extent obliterated, and the wing appears 

 to be a sheet of membrane, more or less rigid, jointed at the 

 base between the tergal and pleural regions of the segment 

 that bears it, where the powerful muscles which either lower 

 or raise the wing (depressors and elevators) find their attachment. 

 The surface of the wing does not present a uniform aspect ; 

 it is traversed by series of tube-like supporting structures 

 variously known as " nerves," " veins " or " ribs ", but for 

 which the term nervures is preferable.. 



In the grasshopper we notice that the two wings on the 

 same side (Fig. i A) differ markedly from each other. The fore- 

 wing (Fig. 7), carried on the mesothorax, is of firm texture, 

 rigid and brittle, elongate and narrow, with almost straight 

 edges and a rounded tip. The hindwing on the metathorax, 

 is more delicate, and may be described as subtriangular with 

 the corners rounded ; when extended from the body, its front 

 margin is fairly straight and the area of the wing next this 

 is more rigid than that region which, lying behind and nearer 

 to the abdomen, can be folded fan wise beneath the firmer 

 forward area. When the wings, not in use for flight, are laid 

 back over and alongside the body (Fig. i B), the forewings 

 completely hide and protect the comparatively delicate hind- 

 wings, that are partly folded beneath them. In the grass- 

 hoppers and their near allies the wings of both pairs are 

 serviceable for flight, though the forewings are, as we have 



1 J. H. Comstock : " The Wings of Insects ". Ithaca, New York, 1918. 



