84 AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 



force mamfesting its potentiality, not in its own inner working, but in its outgoings 

 among the equibrating forces around, and thus offering us, through the known and 

 physical, some measure of the vital within the germ. It is therefore one of the 

 richest sources of truth open to our search. 



The limits of variation it may be difficult to define among species that have 

 close relations. But being sure that there are limits — that science, in looking for 

 law and order written out in legible characters, is not in fruitless search, we need 

 not despair of discovering them. The zoologist, gathering shells or mollusks from 

 the coast of eastern America and that of Japan, after careful study, makes out his 

 lists of identical species, with the full assurance that species are definite and stable 

 existences ; and he is even surprised with the identity of characters between the 

 individuals of a species gathered from so remote localities. And as he sees zoolo- 

 gical geography rising into one of the grandest of the sciences, his faith in species 

 becomes identified with his faith in nature and all physical truth. 



If then we may trust tbis argument from general truths to special, — general 

 truths I say, ft)r general principles as far as established are truths — we should 

 conceive of a species from the potential point of view, and regard it as — 



a. A concentrated unit of force, an ineifaceable component of the system of 

 nature; but 



b. Subject to greater or less librations, according to the universal law of mutual 

 reaction or sympathy among forces. 



And, in addition, in the organic kingdom, 



c. Exhibiting its potentiaUty not simply or wholly in any existing condition or 

 action, but through a cycle of growth from the primal germ to maturity, when the 

 new germ comes forth as a repetition of the first to go another round in the cycle 

 and perpetuate the original unit ; and, therefore, as follows from a necessary per- 

 petuity of the cycle — 



d. Exhibiting identity of species among individuals by perpetuated fertile inter- 

 mixture in all normal conditions, and nonidentity by the impossibility of such 

 intermixture, the rare cases of continuations for one or two generations, attesting 

 to the stability of the law, by proving the effort of nature to rid herself of the 

 Sibnormity, and her success in the effort. 



e. The many like individuals that are conspecific do not properly constitute the 

 species, but each is an expression of the species in its potentiality under some one 

 phase of its variables ; and to understand a species, we must knjw its law through 

 all its cycle of growth, and its complete series of librations. 



We should therefore conceive of the system of nature as involving, in its idea, 

 a system of units, finite constituents at the basis of all things, each fixed in law; 

 these units in organic nature as adding to their kinds by combinations in definite 

 propositions ; and those in organic nature adding to their numbers of representative 

 Individuals, but not kinds, by self-reproduction ; and all adding to their varieties 

 by mutual reaction or sympathy. Thus from the law within and the law without, 

 under the Being above as the Author and sustainer of all law, the world has its 

 diversity, the Cosmos its fullness of beauty. 



I would remark again that we must consider this mode of reaching truth, by 

 reasoning from the general to the special, as requiring also its complement, direct 

 observation to give unwavering confidence to the mind ; and we should therefore 

 eacourage research with a willingness to receive whatever results come from 



