5o8 



NA TURE 



[September 24, 1896 



in the Carboniferous. Although placed in an Order (Archipoly- 

 poda) separate from those of living Myriapods. these species are 

 by no means primitive, and do not supply any information as to 

 the sie])s by which the Class arose. The imperfection of the 

 record is well seen in the traces of this Class ; for between the 

 Carboniferous rocUs and the Oligocene there are no remains of 

 undoubted Myriapods. 



We now come to the consideration of insects, of which an 

 adequate discussion would occupy a great deal too much of your 

 time. An iminense number of species are found in the Pala;ozoic 

 rocks, and these are considered by Scudder, the great authority 

 on fossil insects, to form an Order, the Paheodictyoptera, dis- 

 tinct from any of the existing Orders. The l,atter, he believes, 

 were evolved from the former in Mesozoic times. These views 

 do not appear to derive support from the wonderhil discoveries 

 of M. Brongniart ' in the Upper Carboniferous of Comnientry 

 in the Department of Allier in Central France. Concerning 

 this marvellous assemblage of species, arranged by their dis- 

 coverer into 46 genera and loi species, Scudder truly says : 



" Our knowledge of Pakieozoic insects will have been in- 

 creased three or fourfold at a single stroke. . . . No former 

 contribution in this field can in any way compare with it, nor 

 even all former contributions taken together." (S. H. Scudder, 

 Ant. Joitrn. Sci.y vol. xlvii., February 1894, Art. viii.) 



When we remember that the group of fossil insects, of which 

 so much can be affirmed by so great an authority as Scudder, 

 lived at one time and in a single locality, we cannot escape the 

 conclusion that the insect fauna of the habitable earth during the 

 whole Paktozoic period was of immense importance and variety. 

 Our knowledge of this single group of species is largely due to 

 the accident that coal-mining in Commentry is carried on in the 

 open air. 



Now, these abundant remains of insects, so far from upholding 

 the view that the existing orders had not been developed in Paloeo- 

 zoic times, are all arranged by Brongniart in four out of the nine 

 orders into which in.sectsareusually divided, viz. the Orthoptera, 

 Neuroptera, Thysanoptera, and Homoptera. The importance 

 of the discovery is well seen in the Neuroptera, the whole known 

 Palaeozoic fauna of this order being divided into 45 genera and 

 99 species, of which 33 and 72 respectively have been found at 

 Commentry. 



Although the Carboniferous insects of Commentry are placed 

 in new f;\milies, some of them come wonderfully near those into 

 which existing insects are classified, and obviously form the pre- 

 cursors of these. This is true of the Blattida;, Pliasmida;, 

 Acridiid;x;, and Locustida' among the Orthoptera, the Perlidfe 

 among the Neuroptera, and the Fulgorido; among the Hom- 

 optera. The differences which separate these existing families 

 from their Carboniferous ancestors are most interesting and in- 

 structive. Thus the Carboniferous cockroaches possessed ovi- 

 positors, and probably laid their eggs one at a time, while ours 

 are either viviparous or lay their eggs in a capsule. The Proto- 

 phasmido: resemble living species in the form of the head, 

 antenna:, legs, and body ; but while our species are either wing- 

 less or, with the exception of the female Phyllid;^, have the 

 anterior pair reduced to tegniina, useless for flight, those of 

 Palaeozoic times possessed four well-developed wings. The 

 forms representing locusts and grasshoppers (Pala;acridid;i;) pos- 

 sessed long slender antenna; like the green grasshoppers 

 ( LocustidicUv), from which the Acridiida; are now distinguished 

 by their short antenmv. The divergence and specialisation 

 which is thus shown is amazingly small in amount In the vast 

 period between the Upper Carboniferous rocks and the present 

 day the cockroaches have gained a rather different wing vena- 

 tion, and have succeeded in laying their eggs in a manner rather 

 more specialised than that of insects in general ; the stick insects 

 and leaf insects have lost or reduced their wings, the grass- 

 hoppers have shortened their antenna;. These, however, are 

 the insects which most closely resemble the existing species ; let 

 us turn to the forms which exhibit the greatest differences. 

 Many s]iecies have retained in the adult state characters which 

 are now confined to the larval stage of existence, such as the 

 presence of tr.acheal gills on the sides of the abdomen. In some 

 the two membranes of the wing were not firmly fixed together, 

 so that the blood could circulate freely between them. <Jn the 

 other hand, they are not very firmly fixed together in existing 

 insects. Another important point was the condition of the three 



1 Charles Brongniart — " Recherches pour servir i I'Histoire des Insectes 

 fossiles des temps primaires, pric^d^es d'unc Etude sur la nervation des ailes 

 des Insectes." 1894. 



NO. 1404, VOL. 54] 



thoracic segments, which were quite distinct and ■ separate, 

 instead of being fused as they are now in the imago stage. This 

 external difference probably also extended to the nervous system, 

 so that the thoracic ganglia were separate instead of concen- 

 trated. The most interesting distincticm, however, was the 

 possession by many species of a pair of prothoracic appendages 

 much resembling miniature wings, and which especially suggest 

 the appearance assumed by the anterior pair (tegmina) in exist- 

 ing Phasmida-. There is some evidence in favour of the view 

 that they were articulated, and they exhibit what appears to be 

 a trace of venation. Brongniart concludes that in still earlier 

 strata, insects with six wings will be discovered, or rather insects 

 with six of the tracheal gills sufficiently developeil to serve as 

 parachutes. Of these, the two posterior pair developed into the 

 wings as we know them, while the anterior pair degenerated, 

 some of the Carboniferous in.sects 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 exist- 

 ing species, but it was especially the case with the Protodonata, 

 some of these giant dragon-flies measuring over two feet in the 

 expanse of the wings. 



As regards the habits of life and metamorphoses, Brongniart 

 concludes that some species of Protoephemerida-, Protoperlida;, 

 &c. , obtained their food in an aquatic larval stage, and did not 

 require it when mature. He coricludes that the Protodonata fed 

 on other animals, like our dragon-flies ; that the Palaacridida; 

 were herbivorous like our locusts and grasshoppers, the Proto- 

 locustida; herbivorous and animal feeders like our green grass- 

 hoppers, the Pakxeoblattida; omnivorous like our cockroaches. 

 The Homoptera, too, had elongated sucking 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 

 probable that the majority of these insects lived near the water 

 and their larva; 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 

 insect structure which has taken place .since Carboniferous times. 

 All the great questions of metamorphosis, and of the .structures 

 peculiar to insects, appear to have been very much in the posi- 

 tion in which they are to-day. It is indeed probable enough 

 that the orders which zoologists have always recognised as com- 

 paratively modern and specialised, such as the Lepidoptera, 

 Coleoptera, and Hyirienoptera, had not come into existence. 

 But as regards the emergence of the Class from a single primitive 

 group, as regards its approximation 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 

 specialised members of the Class, and some slight evolution in 

 the rest. Such evolution is of importance as giving us some 

 vague conception of the rate at which the process travels in this 

 division of the Arthropoda. If we look r)x>n development as 

 a series of paths which, by successively uniting, at length meet 

 in a common point, then some conception of the position of that 

 distant centre may be gained by measuring the angle of diverg- 

 ence and finding the number of unions which occur in a given 

 length. In this case, the amount of approximation and union 

 shown in the interval between the Carboniferous period and the 

 present day is relatively so small that it would require to be 

 multiplied many times before we could expect the lines to meet 

 in the common point, the ancestor of in.sects, to say nothing of 

 the far more distant past in which the Tr.acheate Arthropods 

 met in an ancestor presenting many resemblances to Peripatus. 

 But it must not be forgotten that all this vast undefined period 

 is required for the history of one of the two grades of one of the 

 three branches of the whole Phylum. 



Turning now to the brief consideration of the second grade of 

 Arthropods, distinguished from the first grade by the absence of 

 antenna^ the Trilobites are probably the nearest approach to an 

 ancestral form met with in the fossil state. Now that the 

 possession of true antenna; is certain, it is reasonable to sup- 

 pose that the Trilobites represent an early Class of the Aceratous 

 branch which had not yet become Aceratous. They are thus of 

 the deepest interest in helping us to understand the origin of the 

 antennaless branch, not by the ance.str.al absence, but by the loss 

 of true antenna- which formerly existed in the group. But the 

 Trilobites did not themselves originate the other Classes, at any 



