404 DARWINISM chap. 



in the Oolite ; while ants, rej)resenting the highly specialised 

 Hymenoptera, have occiured in the Piirbeck and Lias. 



This remarkable identity of the families of very ancient 

 with those of existing insects is quite comparable with the 

 apparently sudden appearance of existing genera of trees in 

 the Cretaceous epoch. In both cases we feel certain that we 

 must go very much farther back in order to find the ancestral 

 forms from which they were developed, and that at any 

 moment some fresh discovery may revolutionise our ideas as 

 to the antiquity of certain groups. Such a discovery was 

 made while Mr. Scudder's work was passing through the press. 

 Up to that date all the existing orders of true insects appeared 

 to have originated in the Trias, the alleged moth and beetle of 

 the Coal formation ha^-ing been incorrectly determined. But 

 now, undoubted remains of beetles have been found in the Coal 

 measures of Silesia, thus supporting the interpretation of the 

 borings in carboniferous trees as ha\*ing been made by insects 

 of this order, and carrying back this highly specialised form of 

 insect life well into Palseozoic times. Such a discovery renders 

 all speculation as to the origin of true insects premature, 

 because we may feel sure that all the other orders of insects, 

 except perhaps hymenoptera and lepidoptera, were contempo- 

 raneous with the highly specialised beetles. 



The less highly organised terrestrial arthropoda — the 

 Arachnida and Myriapoda — are, as might be exjDected, much 

 more ancient. A fossil spider has been found in the Carboni- 

 ferous, and scorpions in the Upper Silurian rocks of Scotland, 

 Sweden, and the United States. Myi'iapoda have been found 

 abundantly in the Carboniferous and Devonian formations ; 

 but all are of extinct orders, exhibiting a more generalised 

 structure than living forms. 



Much more extraordinary, however, is the presence in the 

 Palaeozoic formations of ancestral forms of true insects, termed 

 by Mr. Scudder Palteodictyoptera. They consist of general- 

 ised cockroaches and walking-stick insects (Orthopteroidea) ; 

 ancient mayflies and allied forms, of which there are six 

 families and more than thirty genera (Neuropteroidea) ; three 

 genera of Hemipteroidea resembling various Homoj^tera and 

 Hemiptera, mostly from the Carboniferous formation, a few 

 from the Devonian, and one ancestral cockroach (Pal^eoblattina) 



