ORIGIN OF LOWEST ORGANISMS. 13 



modified in shape and form even more than the most 

 changeable crystals under the influence of altering 

 " conditions." We should have no longer to do with 



o 



the members of a stable species, which had been repro- 

 ducing its like through countless geologic ages anterior 

 to the advent of man upon the earth. Indeed, in 

 order to reconcile such a possibility with the seem- 

 ingly contradictory fact of the known extreme change- 

 ability of these lower forms of life, we hear only vague 

 hints thrown out about our imperfect knowledge of 

 the "limits within which species may vary." As if, in 

 the face of what we do know concerning hereditary 

 transmission, this changeability did not make it 

 almost impossible to conceive that there should have 

 been an unbroken series of such organisms since that 

 remote epoch of the earth's history, when the first 

 organisms of the kind made their appearance. It does 

 not seem to me that the presumed permanence of a 

 very changeable organism is consistent with, or ren- 

 dered more explicable by, the supposition that some 

 representatives of the species have constantly been 

 undergoing progressive modifications which have been 

 successively perpetuated by inheritance, in the shape 

 of distinct specific forms. Why should some be pre- 

 sumed to have undergone so much change, whilst 

 others (presenting an equal and an extreme degree of 

 modifiability, even to the present day) are supposed 

 to have preserved the same specific form through a 

 countless series of changing influences ? 



