88 



whether a particular form is a variety or a species. But that does not 

 prove that varieties and species are essentially undistinguishable. 

 Every man was originally a boy; and there is a certain period during 

 which it is difficult to say whether a particular individual is man or 

 boy; but that does not prove that manhood is undistinguishable from 

 boyhood. For myself, more than a year before I published on the 

 subject of "Phytophagie species," I announced it as my opinion 

 that the meaning of the term "distinct species" was simply 

 "those that do not now in general mix sexually together, or, if geo- 

 graphically separated, would not do so, supposing them to be placed 

 in juxtaposition ;" and that "the only valid practical criterion of spe- 

 cific distinctness is the general non-existence, either actually ascer- 

 tained or analogically inferred, of intermediate grades in the dis- 

 tinctive characters, whence we may reasonably infer that the two sup- 

 posed species are distinct." {Proceedings Entomological Society 

 Philadeipliia, 1863, II., p. 230.) Tt is in this sense, and in this 

 sense only, that I have ever used the term "species ;" and to call such 

 a definition an "assumption" seems to me much the same thing as 

 saying that Euclid assumes a fact, when he defines a circle as a plane 

 figure having all its external points equidistant from a given internal 

 point. 



But to return from this tedious digression : — It has long been a 

 puzzle to Naturalists, why the Plum Curculio should cut the well- 

 known crescent-shaped slit in the fruit, and why a round hole would 

 not answer its purpose equally well. Harris and Fitch and other 

 authors tell us, that "it first makes a small, crescent-shaped incision 

 with its snout in the skin of the plum, and then, turning round, in- 

 serts an egg in the wound."* Misled by these authorities, and never 

 having personally examined into the point, I copied their statements 

 in my Paper on the Curculio. But Mr. F. C. Hill, of Ohio, has since 

 shown, that we have all of us been in the wrong, and that the Cur- 

 culio first of all bores a round hole with her snout, "not straight in, 

 but slanting backwards, so that the cavity is just below the skin, then 

 deposits lier egg in the hole, and then cuts the usual crescent-slit in 

 front of it, so as to undermine the egg and leave it in a kind of flap, 

 formed by the little piece of the' flesh of the fruit which she has un- 

 dermined." {Prac. Entomol. II. p. 115.) Mr. Hill very acutely 

 suggests, that the object of this complicated process is, "to wilt the 

 piece around the egg and prevent the growing fruit from crushing it ;" 



*See Harris's Injurious Insects, p. 76, and Fitch's Address on the Cur- 

 culio, p. 18. 



