PALAEONTOLOGY 179 



Iii the more recent rocks Insect remains become compara- 

 tively numerous, and in Mesozoic strata forms that can satisfac- 

 torily be referred to existing Orders are found, the Palaeodicty- 

 optera of Goldenberg and Scudder having mostly disappeared ; 

 the Blattidae or cockroaches do not apparently present any great 

 discontinuity between their Palaeozoic and Mesozoic forms. The 

 Tertiary rocks afford us fairly satisfactory evidence to the effect 

 that Insects were then more numerous in species than they 

 are at the present day. At Florissant in Colorado the bed 

 of an ancient lake has been discovered, and vast quantities of 

 Insect remains have been found in it, the geographical conditions 

 indicating that the creatures were not brought from a distance, 

 but were the natural fauna of the locality ; and if so we can 

 only conclude that Insects must have been then more abundant 

 in species than they are now. 



Scudder has informed us l that not only were Insects abundant 

 in the Tertiaries, but that their remains indicate conditions of 

 existence very similar to what we find around us. " Certain 

 peculiarities of secondary sexual dimorphism accompanying 

 special forms of communistic life, such as the neuters and workers 

 in Hymenoptera and the soldiers among the Termitina, are also 

 found, as would be expected, among the fossils, at least through 

 the whole series of the Tertiaries. The same may be said of 

 other sexual characteristics, such as the stridulating organs of the 

 Orthoptera, and of peculiarities of oviposition, as seen in the 

 huge egg-capsules of an extinct Sialid of the early Tertiaries. 

 The viviparity of the ancient Aphides is suggested, according to 

 Buckton, by the appearance of one of the specimens from the 

 Oligocene of Florissant, while some of the more extraordinary 

 forms of parasitism are indicated at a time equally remote by the 

 occurrence in amber of the triunguliii larva of Meloe, already 

 alluded to, and of a characteristic strepsipterous Insect ; not only, 

 too, are the present tribes of gall-making Insects abundant in the 

 Tertiaries, but their galls as well have been found." 



remains, which are often surprisingly perfect. This is one of the reasons that have 

 induced us to prefer a classification of Insects iu which the nature of the wings is 

 considered of great value. It would be impossible to refer fossil Insects to groups 

 that are established on account of the metamorphosis or of the internal structure of 

 their components, for there is not yet any evidence on either of these points in the 

 fossil remains preserved for us by the rocks. 



1 Bull. U.S. Geol. Survey, No. 31, 1886, p. 109. 



