2688 Insects. 



§ 5. Anatomy of the Pro-, Meso- and Metathorax of Stylo ps. 



The prothorax is a short transverse ring, about half the width of 

 the head, increased, as I have described it, by the projecting eyes ; 

 and as the mesothorax is of nearly similar proportions, the insect thus 

 acquires a somewhat hammer-headed figure : the prothorax has on 

 each side a longitudinal sinus or depression, which separates the dor- 

 sal from the sternal surface ; at this sinus the dorsal surface slightly 

 projects, somewhat overhanging the sternal : the propedes are distant 

 at the base, simple, having the coxae longer than the femora, and both 

 these joints slightly incrassated : the tibiae are rather longer than 

 either of the preceding joints, are slightly thickened exteriorly, and 

 are perfectly simple and unarmed, having no spines or other appen- 

 dages: tarsi four-jointed, the joints deeply notched and cushioned 

 beneath ; claws none.* 



The mesothorax is also a short transverse ring, rather wider than 

 the prothorax : it is divided dorsally, by two slight furrows, into 

 three sections : the dorsal surface is flat centrally, but slopes off on 

 each side, and overhangs the lateral surface like the roof of a house : 

 attached to this segment, near its anterior margin and on its sloping 

 or deflected sides, are two opaque, leathery, narrow, diminutive, 

 slightly curved, rudimentary wings : t these organs, like the elytra of 

 Coleoptera generally, and the halteres of Diptera, are without the 

 characteristics of normal wings, but, as in both these instances, their 

 attachment to a certain segment removes all doubt as to their true 

 nature. This segment also bears the mesopedes, which differ from 

 the propedes only in their shorter coxae. 



The metathorax is enormously developed, and comprises nearly 

 two-thirds of the entire insect : its surface exhibits numerous well- 

 marked divisions, but it is to be regretted that existing figures and 



* This description of the tarsi is perhaps conventional rather than absolute : it 

 has been said that a fifth joint had been observed on the pro- and mesotarsi, but that 

 these — being very slender and fragile — have been detached through entanglement in 

 the fabric of the material employed for making the net, whenever the insect may have 

 been taken. 



f The term twisted, as applied to these organs, although not positively erroneous 

 (since they are not perfectly straight), still conveys an erroneous idea, — since that 

 word, as used in several generic names, implies a complete and somewhat corkscrew- 

 like twisting, and not the deviation from a direct line observable in the fore wings of 

 Stylops. 



