1804.] 648 



(•omplete teats like a Mammal. We see the last steps of the process, 

 by which Land Birds have been developed out of Aquatic Birds, in the 

 European Water-ou.sel, which is a true Thrush and yet dives like a 

 Loon ; and we see the beginnings of the same process in the N. A. 

 wood-duck (Anas sponsa), which is a true Duck and yet habitually 

 perches upon trees and builds in the holes of trees. We see the ulti- 

 mate steps, by which insectivorous aquatic Coleoptera have been con- 

 verted into insectivorous terrestrial Toleoptera, in the Greodephagous 

 genus OmophroH, which has the shape and the general appearance of 

 the Hydradephagous genus Bj/ drop or us [11//;/ rot us), and to this day is 

 always found on the borders of streams. We see the same thing in the 

 Geodephagous Oodes Jluvialis Lee, which I often find adhering to the 

 under surface of partly submerged logs, and which, w^hen endeavoring 

 to escape, generally makes for the water, and as soon as it has reached 

 it dives out of sight in a moment like any Coli/mJiftes. We see the 

 incipient steps of the same process in the European Hydradephagous 

 genus Pclohius. wdiich inhabits the water and yet has gressorial legs 

 like a Carabus, and. unless my recollection of P. Hermanni deceives 

 me. has also a distinct neck, like most Greodephaga, except Omophron. 

 and unlike most Hydradephaga, except Hidiplus and Cnemidotus. But 

 in all these, and a hundred similar cases, the vSteps by which the process 

 is accomplished are slow and gradual, and there is no sudden leap, as 

 there would be if a Duck had teats and save suck, or if a Bear laid ejrKs 

 and incubated them, or if one Cecidomi/ia copulated and laid eggs in 

 the normal manner in the imago state, and another Ceridomyla was 

 viviparous by parthenogenesis in the larva state. I do not contend that 

 there is never any difference in the habits of the species comprehended 

 under a given genus, but only that there is never any radical and fun- 

 damental difference, of such a nature, for example, as that there can 

 scarcely exist any intermediate grades between the normal and the dif- 

 fering forms. Now an insect, if it procreate at all, must procreate either 

 in the larva, or in the pupa, or in the imago state, and there cannot 

 scarcely be any intermediate grades between these three. Therefore I 

 maintain that no two of these three can co-exist in one and the same 

 genus, Cecidomi/ia. 



Another thing. It appears that these supposed young Cecidomyious 

 larvae, which are said by Wagner and othars to be vivip irously p.'o- 



