November 6, 1896.] 



SCIENCE. 



677 



are the insects whicli most closely resemble 

 the existing species; let us turn to the 

 forms which exhibit the greatest differences. 

 Many species have retained in the adult 

 state characters which are now confined to 

 the larval stage of existence, such as the pres- 

 ence of tracheal gills on the sides of the ab- 

 domen. In some the two membranes of the 

 wing were not firmly fixed together, so that 

 the blood could circulate freely between 

 them. On the other hand, they are not very 

 firmly fixed together in existing insects. 

 Another important point was the condition 

 of the three thoracic segments, which were 

 quite distinct and separate, instead of being 

 fused as they are now in the imago stage. 

 The external difference probably also ex- 

 tended to the nervous system, so that the 

 thoracic ganglia were separate instead of 

 concentrated. The most interesting distinc- 

 tion, however, was the possession by many 

 species of a pair of prothoracic appendages 

 much resembling miniature wings, and 

 which especially suggest the appearance as- 

 sumed by the anterior pair (tegmina) in 

 existing Phasmidse. There is some evi- 

 dence in favor of the view that they were 

 articulated, and they exhibit what appears 

 to be a trace of venation. Brongniart con- 

 cludes that, in still earlier strata, insects 

 with six wings will be discovered, or rather 

 insects with six of the tracheal gills sufB.- 

 ■ciently developed to serve as parachutes. 

 Of these, the two posterior pair developed 

 into wings as we know them, while the 

 anterior pair degenerated, some of the Car- 

 boniferious insects presenting us with a 

 stage in which degeneration had taken 

 place but was not complete. 



One very important character was, as I 

 have already pointed out, the enormous size 

 reached by insects in this distant period. 

 This was true of the whole known fauna as 

 compared with existing species, but it was 

 especially the case with the Protodonata, 

 some of these giant dragon-flies measur- 



ing over two feet in the expanse of the 

 wings. 



As regards the habits of life and meta- 

 morphoses, Brongniart concludes that some 

 species of Protoephemeridse, Protopelidse, 

 etc., obtained their food in an aquatic larval 

 stage and did not require it when mature. 

 He concludes that the Protodonata fed on 

 other animals, like our dragon-flies; that 

 the Palseacridiidse were herbivorous like 

 our locusts and grasshoppers, the Protolo- 

 custidse herbivorous and animal feeders 

 like our green grasshoppers, the Palseo- 

 blattidse omnivorous like our cockroaches. 

 The Homoptera, too, had elongated suck- 

 ing mouth-parts like the existing species. 

 It is known that in Carboniferous times 

 there was a lake with rivers entering it, at 

 Commentry. From their great resemblance 

 to living forms of known habits, it is prob- 

 able that the majority of these insects lived 

 near the water and their larv£e in it. 



When we look at this most important 

 piece of research as a whole, we cannot fail 

 to be struck with the small advance in in- 

 sect structure which has taken place since 

 Carboniferous times. All the great ques- 

 tions of metamorphosis, and of the struct- 

 ures peculiar to insects, appear to have 

 been very much in the position in which 

 they are to-day. It is, indeed, probable 

 enough that the Orders which zoologists 

 have always recognized as comparatively 

 modern and specialized, such as the Lepi- 

 doptera, Coleoptera and Hymenoptera, had 

 not come into existence. But as regards 

 the emergence of the Class from a single 

 primitive group, as regards its approxima- 

 tion towards the Myriapods, which lived at 

 the same time, and of both towards their 

 ancestor Peripatus, we learn absolutely 

 nothing. All we can say is that there is 

 evidence for the evolution of the most 

 modern and specialized members of the 

 Class, and some slight evolution in the rest. 

 Such evolution is of importance as giving 



