SOUTH Al'RlCAN TEKMITES. 25 



uiid quite eoimuoiily entirely absent on the outer (distal) edge 

 of the Aving." What else is said has but to do with an 

 imagined ontogeny. The point is that the termite wing does 

 possess a marginal rib, which is pronounced along the outer 

 margin and often more or less faded out along the inner ; it 

 is, in no conceivable manner, derivable from an innnediate or 

 remote tracheal forerunner. 



Among earlier writers. Frit/. Miiller, Spider, iJrauer, and 

 Redtenbacher claimed that the wing-ribs arose from pre- 

 existing tracliea3 except, they held, that the outermost or costa 

 did not have a trachea as its origin and therefore had nothing 

 to do with the " veins." Comstock and Needliam,^ in a very 

 able and convincing demonstration, seemingly succeeded in 

 shoAvino- that all the ribs, including' the costa, were in the 

 beginning preceded by tracheie ; unfortunately, they give no 

 particulars of their studies of the wing tracheie of Termites, 

 otherwise I might have found no difficulty in reconciling 

 myself to their view. Their studies enabled them to make 

 the following definite announcement : " It can be accepted as 

 a firmlj'-established fact that the courses of the wing-veins of 

 primitive insects were determined by the courses of the pre- 

 existing tracheie." So far as termite wings are concerned, 

 the studies now submitted will show that those ribs that are 

 })receded by tracheie reflect the courses and developments of 

 those tracliea> ; and, the more generalised the wings, the 

 more is the individuality of a pre-existing trachea recorded in 

 the final wing. The studies, however, controvert the doctrine 

 that the costa is also preceded by a trachea. 



As one of the main features of their thesis, these authors 

 put forward " a hypothetical ty]}e to which the wings of all 

 orders might be referred," They indicated the primitive 

 condition of the basal connections of the wing-tracheie and 

 devised two routes of specialisation, one of addition, the 

 other of reduction. 



The hypothetical type was " represented by the trache;e 



' Comstofk. J. H., and Needham. J. G.. " The Wiiiys of Insects." 

 ' Tlie American Naturalist," vols, xxxii. xxxiii. 



