2690 Insects. 



Tridactylus and Acridium. The wings of Stylops fold more like 

 drapery when suspended : they have a strong costal nervure, and a 

 few very delicate and obscure discoidal nervures, but are quite with- 

 out regular radiating nervures, which characterise the fan-like wings 

 of Orthoptera. The metapedes are simple, situate near the posterior 

 margin of the metasternum, and differ chiefly from the pro- and meso- 

 pedes in their shorter tibiae and in their closely approximate insertion. 

 The remaining segments of the insect are eight in number, and dif- 

 fer from those described in being soft and flexible, and capable of 

 being twisted about in all directions, turning over the back with ease 

 and agility : each of these segments — except the last, which appears 

 to be the male organ of generation — is most distinctly divided longi- 

 tudinally into four surfaces, — a dorsal, a sternal and two pleural. 



§ 6. Comparative Anatomy of the Pro-, Meso- and Metatliorax of 



Stylops. 



Many years ago I invited the attention of entomologists to a theory 

 regarding the correspondence in development between the wings and 

 winged segments in insects. I attempted to show that certain condi- 

 tions of the winged segments predicate analogous conditions of the 

 wings. Thus, when the fore wings constitute the real organs of 

 flight, the mesothorax must be capable of imparting their power to 

 these wings, and this power we invariably find to be co-existent with 

 increased bulk, so that the mesothorax is largely developed at the ex- 

 pense of the metathorax. On the contrary, when the hind wings 

 constitute the sole organs of flight, the reverse takes place ; the me- 

 tathorax is then largely developed at the expense of the mesothorax. 

 I hope to be pardoned for the egotism exhibited in a reference to 

 what I have previously done ; but the revival of a theory which, if 

 noticed at the time, was never accepted, and has probably been en- 

 tirely forgotten, seems essential to the proper understanding of the 

 very interesting structure of the wing-bearing segments of Stylops. 

 Although an unfortunate error crept into the first scientific description 

 of Stylops, all entomologists are, I believe, now agreed on the nomen- 

 clature of the winged segments, — the fore wings being attached as 

 always to the mesothorax, the hind wings to the metathorax. The 

 supposition that any connexion existed between the fore wings and 

 fore legs of course implied that both these were prothoracic ap- 

 pendages, and consequently that the entire arrangement of these parts 



