482 Recent freshwater Mollusca 



number of distinguishing points. Moreover, whilst we admit 

 that there may be 500 species of HeHx, we cannot allow the 

 possibility of 200 Ancylus, with the usual amount of character, 

 because the shell is of the most simple form, and deprived 

 of a number of parts and modifications which afford good 

 specific characters in the former genus. It may, indeed, be 

 insisted, that, for all we know to the contrary, one, two, or 

 fifty, species of Ancylus may be hidden under each distinct 

 form, and that, in this manner, there may be as many Ancylus 

 as Helix. To assert that two monomorphic animals, belong- 

 ing to one of the families having uniform tints, are distinct, 

 because, if we could metamorphose them into members of 

 another family, having varying colors, the tints of the two 

 (not being subject to the law of uniformity) might present 

 a specific* variation, is to imagine an organic iso-morphismf 

 of which we have hitherto had no evidence. Admitting, 

 however, that, in an imaginary metamorphosis, two individu- 

 als (none of which are absolutely alike in every point) of a 

 species of Melania, should result in two distinct species of 

 Conus, of different markings and colors, I conceive that we 

 would not be justified, either in assuming the specific difTer- 

 ence of the former, or the identity of the latter, which we 

 derive from them ; because, although, as Conus, they would 

 be distinct from the possession of a different modification of 

 character, as Melania, they must be alike, the characters being 

 identical. Let us now suppose our metamorphosis to take 

 the opposite direction, the subjects being two species of Helix 

 of the same size, form, color, and texture, of shell and ani- 



* " Specific, that makes a thing of the species of which it is ; designating the 

 peculiar properly or properties of a thing, which constitute its species, and distin- 

 guiah it from other things. Specific chak acter, a circumstance or circumstances 

 distinguishing one species from every other species of the same genus." — Web- 

 ster's Diet. It is evident, from these definitions, that, where there is no specific 

 character, there can be no distinct species ; so that, to prevent confusion, it will be 

 necessary for those whose views I am opposing, to adopt some other term, instead 

 of species, to designate wliat they contend for. 



t This term may be introduced into zoology to indicate the resemblance which 

 a parasitic insect bears to another, into whose nest it must be able to penetrate un- 

 observed. 



