178 INSECTS CHAP. 



families dependent throughout the Class Insecta on characters of 

 similar morphological value has, however, scarcely been entered 

 on, and it is perhaps not desirable, seeing how very small a 

 portion of the Insects of the world have been critically examined, 

 that much effort should be yet expended on an attempt of 

 the kind. It must be admitted that the species of Insects should 

 be obtained before they can be satisfactorily classified, and it is 

 estimated l that at least nine-tenths of the Insects of the world 

 are still unknown to entomologists. 



Geological Record. Although Insects have a very long 

 pedigree, it is as yet a very imperfect one. The remains of 

 creatures that can be referred to the Class Insecta have been 

 found, it is said, in Silurian strata ; only one or two of these 

 very early forms are at present known, and the information 

 about tb,em is by no means satisfactory ; if Insects at all as 

 to which some doubt exists they apparently belong to very 

 different forms, though, like all the earliest fossil Insects, they 

 are winged. In the strata of the Carboniferous epoch numerous 

 Insects have been detected, in both Europe and North America. 

 These earlier Insects are by Scudder called Palaeodictyoptera, 

 and separated from the Insects around us on the ground that 

 he considers there existed amongst these palaeozoic Insects no 

 ordinal distinctions such as obtain in the existing forms, but 

 that the primeval creatures formed a single group of generalised 

 Hexapods. Brauer does not accept this view, considering that 

 the earlier Insects can be referred to families existing at the 

 present time and forming parts of the Orthoptera, Neuroptera, 

 and Hemiptera. The discrepancy between these two authorities 

 depends to a great extent on the different classifications of existing 

 Insects that they start from ; Scudder treating the wings as of 

 primary importance, while Brauer assigns to them only a 

 subordinate value. From the point of view taken in the present 

 work Scudder's view appears to be in the main correct, though 

 his expression as to the primary fossil Insects forming a single 

 homogeneous group is erroneous. The Neuroptera, still in exist- 

 ence, certainly form a heterogeneous group, and it is clear that 

 the Palaeozoic fossils represent a more diverse assemblage than 

 the present Neuroptera do. 2 



1 Lord Walsingham, Proc. Ent. Soc. London, 1889, p. Ixxx. 



- We may mention that fossil Insects are chiefly determined from their wing- 



