262 



INSECT TRANSFORMATION 



ferous age, had well-developed wings which served already as 

 efficient organs of flight. 1 But we know that wings arise in 

 exopterygote insects as outgrowths from the second and third 

 thoracic segments, and in Stenodictya (Fig. 124), a fossil 

 insect from the Carboniferous beds of Commentry, France, 

 there are paired, flattened outgrowths on the prothorax and 



FIG 124. A PALAEOZOIC INSECT (Stenodictya lobata). 

 from the Carboniferous of Commentry, France. natural 

 size. After Handlirsch, i Congr. Int. Entom. 1910. 



on eight of the abdominal segments, which, from the aspect 

 and markings, seem to be comparable to wing-rudiments. It 

 has, therefore, been suggested that the ancestors of all winged 

 insects had a series of such paired outgrowths all along the 



arranged in " descending " order, the newer formations above, the older below, 

 as they occur generally in nature : 



Pleistocene. 



Pliocene. 



Miocene. 



Oligocene. 



Eocene. 



TERTIARY OR 

 CAINOZOIC. 



SECONDARY OR 

 MESOZOIC. 



PRIMARY OR 

 PALAEOZOIC. 



Cretaceous. 



Jurassic. 



Trias. 



Permian. 



Carboniferous. 



Devonian. 



Silurian. 



Cambrian. 



1 A. Handlirsch : " Die fossilen Insekten und die Phylogenie der rezenten 

 Formen". Leipzig, 1906-8. J. II. Comstock : "The Wings of Insects". 

 Ithaca, New York, 1918. 



