APHIDES AT FLORISSANT IN COLORADO. 155 



from the Swiss Miocene, from which 876 species of 

 insects have been deduced : 844 of these occur at 

 CEningen. Coleoptera are by far the most abundantly 

 represented, but still the Hemiptera number as many 

 as 136 species.* 



Apterous insects, as a rule, are more rare than 

 winged. Probably they were less drifted by winds, and 

 but little liable to drowning in the shallow waters. 

 Thus, winged ants are in profusion ; some having been 

 killed with their wings yet expanded, whilst the 

 apterous forms are infrequent. It is not improbable 

 that some deleterious gaseous exhalations suddenly 

 passed over these waters. Destruction was so rapid 

 that several examples occur in which males and 

 females remain conjugated; and now they rest together 

 in their silent tombs. t The presence of larvaa shows 

 that insect metamorphosis occurred then, much as 

 it obtains now. 



Although the climate of Miocene times here must 

 have been at least as warm as that of Southern Italy, 

 Aphides disported themselves side by side with large 

 Cicadidee and gigantic water-bugs. Mr. Walker 

 thought that if Aphides exist in tropical climates, they 

 will probably be found to be entirely viviparous, and 

 then there will be no necessity for the egg. But the fact 

 that Aphidian ova are quite as common in the South 

 of France and Italy as in Britain proves that mere 

 temperature has but little to do with the appearance 

 of the true sexes and their issue. 



Several fine examples of Aphis, of Lachnus, and 

 of Pemphigus have been figured by Prof. Heer, some 

 of which I have reproduced in Plate CXXXIL A 

 gall-making Pemphigus clearly attacked the leaves of 

 an ancient kind of poplar tree, and in a manner very 

 similar to that to be observed on our own, and it made 

 the like excrescences. 



* ' Primaeval World,' vol. i, p. 296, et seq. 

 f ' Priru. World,' vol. ii, p. 44. 



