THE PROBLEMS OF TRANSFORMATION 263 



body which may originally have been of service as parachutes, 

 and of these the two pairs on the mesothorax and metathorax 

 became greatly enlarged and hinged on to their segments so 

 as to confer on their possessors the power of flight. It is of 

 interest to note that the larvae of some termites (Coptotermes) 

 have on the prothorax elongate wing-like organs 2 , which 

 disappear in later stages. 



There can, however, be no doubt that the earliest insects 

 known to us developed their wings outwardly, because nymphs 

 with visible wing-rudiments have been recognized among 

 them. Most of them are grouped in an order called the 

 Palaeodictyoptera, characterized by a close similarity between 

 the fore- and hindwings, and by a type of nervuration whence 

 that of the Isoptera, the Plecoptera, and the Orthoptera 

 might alike be derived. Many of the Palaeodictyoptera had 

 the general aspect of cockroaches, and forms of Carboniferous 

 age such as the North American Spaniodera appearing 

 to lead definitely towards the orthopteroid type of wing- 

 differentiation, have been relegated to an order Protorthoptera. 

 Thus the oldest insects, of which remains have been preserved 

 for study, are seen to have been for the most part Exoptery- 

 gota allied to those orders now living in which there is least 

 difference in form between the adult and the young. 



Contemporary with these ancient insects lived some which 

 may be regarded as representing an early type of mayfly 

 the order Protoephemerida of which Platephemera, from the 

 St. John's shales (Upper Carboniferous) of New Brunswick, 

 is the best known. In these primaeval mayflies there 

 was a close similarity between the fore- and the hindwings, 

 and among intermediate forms whose remains are preserved 

 in rocks of Jurassic age, the hindwings are less reduced than 

 those of modern mayflies. As to life-history it must remain 

 questionable if the mayfly-like insects of the Carboniferous 

 underwent transformations similar to those of recent mayflies. 

 But a Permian mayfly-nymph with paired gill-appendages on 

 nine abdominal segments has been preserved for our study in 

 Russian rocks, so the characteristic transformation had become 



2 E. Bugnion and C. Ferriere : " L'Imago du Coptotermes flavus. 

 Larvae portant des Rudiments, d'Ailes Prothoraciques ". Mem. Soc. Zool. 

 France, XXIV. 1911. 



