VARIETIES OF FORM IN THE SAME SPECIES. 



241 



of species, from a trifling difference of form. Molluscous animals, 

 having no internal skeleton, appear to possess great power of adap- 

 tation, and of forming and renewing their shells, according to the cir- 

 cumstances in which they are placed. It therefore seems to be trav- 

 elling far beyond the bounds of sober experience, to establish such 

 sweeping generalizations, on the evidence of shells alone. Where other 

 concurrent evidence can be adduced, either from the organic remains 

 of plants or the higher classes of animals, the presence or absence of 

 certain species of shells may serve conjointly, as distinctive charac- 

 ters of formations; we may farther admit, that the greater abund- 

 ance of supposed species of shells, in any formation, analogous to 

 existing species, implies that the conditions under which the strata 

 were deposited, were analogous to the present condition of the globe 

 whether all the shells designated as different species were really so 

 or not. 



Change of form, much greater than what exists in the coverings 

 of many testaceous animals said to be of different species, may be 

 observed to take place in the same species of mammiferous animals 

 in different countries. The sheep of Africa, of Asia, and of Eu- 

 rope present great varieties of form ; and even in Europe, the dif- 

 ference between one breed of sheep and another, in respect to form, 

 size, or horns, is much greater than between the forms of many dif- 

 ferent species of shells. Let us suppose the race of sheep to be 

 entirely destroyed in some future revolution of the globe, and the 

 skins and horns alone to be preserved in a fossil state, without any 

 portion of the skeleton or of the hoofs or teeth. The future geolo- 

 gist or naturalist would have as much reason to establish specific dis- 

 tinctions from the fossil skins, as the conchologist has to establish 

 them from fossil shells. The external covering is all that can guide 

 either of them ; for of the animals themselves the conchologist knows 

 nothing, absolutely nothing, that can serve for a specific character. 

 The future dealer in fossils might establish forty species or more of 

 the genus Ovis. Thus he would have his Ovis maximus, O. medius, 

 O. minimus, O. lanigerens, O. crinigerens, O. cornutus, O. bicor- 

 nutus, 0. quadricornutus, O. longicaudatiis, O. pinguicaudatus, cum 

 multis aliis. Much ingenious and learned speculation would doubt- 

 less be expended, to prove the epochs in which each species flourish- 

 ed, and to determine the geological ages of the horned, and the fat- 

 tailed sheep. 



Few persons ever made more experiments, for a long series of 

 years, on the change of form and other qualities of animals, that 

 might be permanently produced, than the late Mr. Robert Bakewell, 

 of Dishley in Leicestershire. I have heard him say, that he scarce- 

 ly knew any assignable limits beyond which these changes, both ex- 

 ternal and internal, might not be carried. I am fully convinced that 

 the Author of nature has established laws for the preservation of dis- 

 tinct classes and orders of animals ; but be it ever remembered, that 



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