THE MIGRATION AND DISPERSAL OF INSECTS. 213 



classified with the existing Orders of insects, though not belonging to 

 existing families', and ho refers the oldest known fossils to the 

 Ncuroptera, Orthoptera and llouioptera, the greater part being 

 referable to the first-named Order. The Protcphemerides, Protodonates 

 and Protoperlides of this author may probably be looked upon as the 

 actual ancestors of our existing Ephemeridie, Odonata and Perlidic. 



Compared with the more highly specialisd vertebrates, then, 

 insects have a remarkable ancestry. Many existing forms of insect 

 life are found in the Tertiaries, and the social insects had then already 

 taken on their present form— neuters, workers and soldiers of the 

 Hymenoptera and termites having been found. Even the viviparity of the 

 aphides of this age is suggested by one of the specimens from Floris- 

 sant, and not only are the present tribes of gall-making insects abun- 

 dant in the Tertiaries, but the galls themselves have also been found. 



Going back, we find that many of the present genera of Coleoptera 

 (and probably Lepidoptera) were in existence when Archegosaurus and 

 Ichthyosaurus ruled the sea, and Pterodactyl the air. The main 

 Orders of insects — Hemiptera, Orthoptera, Odonata, Lepidoptera, 

 Hymenoptera, Coleoptera, Diptera — were dift'erentiated long ;eons of 

 time ere this, probably even before the deposition of the Silurian strata, 

 and the ancestry of insects passes into a time, compared with which 

 the ancestry of mammals sinks into insignificance. Our present 

 species have probably largely originated in Pleistocene times, but the 

 more dominant genera of most of the Orders certainly existed at the 

 commencement of the Tertiary period, and certainly extended far back 

 into the Mesozoic or even late Paheozoic times. The points of origin 

 of the Orders are subjects on which the geological record is silent. 

 We only know that many of them must have been in existence when 

 the oldest known sedimentary rocks were deposited. 



This vast antiquity of insects considered in connection with their 

 present tendency to dispersal, makes the study of the insects of any 

 given region a very difficult matter. We have, in almost every region, 

 insects representing an exceedingly ancient fauna, intermixed with 

 comparatively recently introduced forms. The former have, as it 

 were, often been developed from the ancient forms in aitit, the latter 

 have spread at various times extending over a period of time dating 

 from the present day back through Cainozoic, and Mesozoic times, 

 into the lands they now occupy from other regions. The most recent 

 additions are probably those representing the more cosmopolitan species 

 and genera, which have passed at one time and another along every 

 line of migration open to other terrestrial animals, and have also been 

 able to take advantage of other routes, exclusively their own. The 

 older forms have probably survived geographical changes which have 

 caused the extinction of many of the more highly-organised animals. 

 The study of the species that are now active in their movements may 

 lead us to discriminate in some instances the new from the ancient 

 fauna, and give us clues as to the districts where cosmopolitan species 

 originated. 



The position of Pseudopontia (Gonophlcbia). 



By Professor A. EADCLIFFE GKOTE, M.A. 



There exists a difference of opinion as to the classification of 

 Pseudoponfio. Scuddcr asks the ({ucstiou : " Is it a ))uttertly ?" i.e., 



