494 Mr. J. D. Dana on Species. 



a. A concentered unit of force, an ineffaceable component of 

 the system of nature; but 



b. Subject to greater or less librations, according to the uni- 

 versal law of mutual reaction or sympathy among forces. 



And, in addition, in the organic kingdom, 



c. Exhibiting its potentiality 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 perpetuity of the cycle — 



d. Exhibiting identity of species among individuals, by per- 

 petuated fertile intermixture in all normal conditions, and non- 

 identity by the impossibility of such intermixture, the rare cases 

 of continuation for one or two generations attesting to the 

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

 of the abnormity, 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 know its law through all 

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



We should therefore conceive of the system of nature as in- 

 volving, in its idea, a system of units, finite constituents at the 

 basis of all things, each fixed in law ; these units in inorganic 

 nature as adding to their kinds by combinations in definite 

 proportions; 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 sustailaer 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 un- 

 wavering confidence to the mind; and we should therefore 

 encourage research with a willingness to receive whatever results 

 come from nature. We should give a high place in our estimate 

 to all investigation tending to elucidate the variation or per- 

 manence of species, their mutability or immutability; and at 

 the same time, in order that appearances may not deceive us, 

 we should glance towards other departments of nature, re- 

 membering that all truth is harmonious, and comprehensive law 

 the end of science. 



A word further upon our conceptions of species as realities. 



