264 INSECT TRANSFORMATION 



by then established. It will be remembered (p. 181) how the 

 mayfly larva and imago both preserve characters, indicating 

 crustacean affinities, more primitive than can be found in 

 any other group of winged insects, and suggesting that 

 for the ancestors of the order we must probably look near to 

 the base of the exopterygote stock. And this is exactly the 

 conclusion suggested also by the scanty sample of related 

 fossil insects, for the precursors of the mayflies were con- 

 temporary and collateral with the ancestors of orthopteroid 

 insects. 



The same conclusion may be stated with some confidence 

 as regards the dragon-flies. From the coal measures of 

 Commentry, France, a large number of palaeozoic insects 

 have been described, 1 among them the gigantic Meganeura, 

 with a wingspread of more than two feet, and the aspect of 

 a modern dragon-fly, but with the wing-nervuration less 

 remarkably specialized, the radial sector not invading the area 

 of the median nervures as it does in most recent Odonata. 

 These ancient Protodonata, as they are called, persisted into 

 the Permian (the newest sub-division of the Palaeozoic or 

 Primary life-epoch) , to be succeeded in Mesozoic or Secondary 

 times by typical dragon-flies whose remains are preserved in 

 rocks of Liassic and Jurassic age (the famous " lithographic 

 stone " of Solenhofen being especially rich in such fossils), 

 referable not only to the same order (Odonata) as our living 

 dragon-flies, but in most cases to existing sub-families. As 

 to the life-histories of the Carboniferous Protodonata we have 

 no certain knowledge ; it has been suggested that their early 

 instars lived in damp earth rather than in water. But the 

 Mesozoic dragon-flies resemble recent genera so closely that we 

 can have no doubt as to the similarity of their life-histories ; 

 and from the Oeningen beds in southern Germany, of Cainozoic 

 or Tertiary (Miocene) age, a large number of fossil libelluline 

 larvae have been disinterred, of which it is stated that " some 

 had the labial mask projecting, as if in the act of striking their 

 prey ". The dragon-fly stock had thus already made con- 

 siderable progress towards its high development in Carboni- 

 ferous times ; the differentiation between imago and larva 



1 C. Brongniart : " R6cherches pour servir a 1'Histoire des Insectes 

 Fossiles des Temps Primaires ". St. fitienne, 1893. 



