164 THOUGHTS ON SPECIES. 



agents, is there a single fact in physiological science which 

 justifies the belief, that they influence cell-development in any 

 other manner save that of disease, leading not only to the 

 extermination of the individual but of its progeny ? 



Contemplate the climatal changes and the altered facilities 

 of obtaining sustenance as taking place almost insensibly, 

 and extending their range of effects into geological periods, 

 adding isolation to intensify their influence, and where must 

 permanent variation of species, or the tendency to change 

 indefinitely, have its inception ? Beyond doubt, as the ad- 

 vocates of the latter doctrine especially claim, in the cell-action 

 of the reproductive system. If this is capable of undergoing 

 any other change than that which produces monstrosities, 

 organisms are thus successively and insensibly altered b}^ 

 almost imperceptible modifications, until in the course of 

 ages nothing remains to them that was originally specific, 

 and, by parity of reasoning, nothing that was generic, or 

 tribal, or ordinal, or pertaining to classes. Thus when it is 

 once admitted that modification may take place in any organ 

 or part essential in specific life, there is no limit to what may 

 take place under the supposed operation of physical influ- 

 ences. All closely allied forms cease to be the object of 

 special design ; special creation itself becomes problematical, 

 since, under this view, the primitive germs themselves may 

 have originated from the accidental combinations of inorganic 

 matter. But the physiological truth of the question lies in 

 the incapability of germ-cells to vary from their specific plan 

 of ultimate development. And although the ovum has 

 formed an integral part of an antecedent form, the structural 

 evolution of a perfect being from it, or the germinal capacity 

 of the ovum, does not represent the parent or organism pro- 



