406 [November 



and the female has in no case intercrossed with a male belonging to a 

 different Phytophagic Variety, then it is probable that habit will have 

 become a second nature, and that it will cease to be possible for that 

 insect, which by the supposition has fed upon that one plant for a very 

 long series of years, to feed upon any other plant than that to which it 

 has become habituated by the Laws of Inheritance. 



But before this point is reached, another series of phenomena will 

 have come into play. Every naturalist is aware that species often run 

 into what are known as geographical races, when separated into two or 

 more distinct groups by physical barriers. Just so the Phytophagic 

 Variety, having by the supposition been isolated from the other mem- 

 bers of its species, will often run into what may be called Phytophagic 

 Races, and finally perhaps acquire either a moral indisposition, or a 

 physical inability, to intercross with the other members of the species. 

 It will then have become what I propose to call a Phytophagic Species, 

 distinguished from the other members of the species to which it originally 

 belonged by certain slight peculiarities of size, or of coloration, or occa- 

 sionally even of structure, just as geographical races are so distinguished. 

 But there will be this essential difference between the two cases: Geo- 

 graphical Races are connected, or supposed to be connected, by all the 

 intermediate grades, and may therefore be reasonably concluded to in- 

 tercross on the confines of their geographical boundaries. Phytophagic 

 Species are not so connected, and by the supposition they do not inter- 

 cross, or, at all events, only in very rare instances, as is sometimes the 

 case with what are allowed on all hands to be distinct species.* 



According to my views, Phytophagic Species are as truly distinct 

 species as those which differ by much stronger characters. "The only 

 valid practical criterion," as I have already said, {Proc. Ent. Soc. Phil. 

 II. p. 220,) " of specific distinctness is the general non-existence, either 

 actually ascertained or analogically inferred, of intermediate grades in 

 the distinctive characters, whence we may reasonably conclude that the 

 two supposed species are distinct, i. e. that they do not now in general 



•••■Mr. Henry Shinier, of Carroll County, Illinois, writes me word that he has 

 recently seen %, Hippodamia maculata DeGeer copulating with 9 Coccindla no- 

 vemnotata Hbst. He has sent me specimens of both species, and I have no doubt 

 that they were rightly determined by him. Similar examples in this family 

 have already been referred to by me. {Froc. Ent. Soc. Phil. I. p. .351.) 



