AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 85 



nature. We should give a high place in our estimate to all investigation tending 

 to elucidate the variation or permanence of species, their mutability or immutabi- 

 lity ; and at the same time, in order thac appearances may not deceive us, we 

 should glance towards other departments of nature, remembering that all truth is 

 harmonious, and comprehensive law the end of science. 



A -word further upon our conception of species as realities. In acquiring the 

 first idea of species, we pass, by induction, as in other cases of generalization, from 

 the special details displayed among individuals to a general notion of a unity of 

 type ; and this general notion, when written out in words, we may take as an 

 approximate formula of the species. One system of philosophy thence argues that 

 this result of induction is nothing but a notion of the mind, and that species are 

 but an imaginary product of logic ; or at least, that since, as they say, (we do not 

 now discuss this point), genera are groupings without definite limits which may be 

 laid off variously by different minds, so species are undefined, and individuals are 

 the only realities — the supposed limits to species being regarded as proof of partial 

 study, or a consequence of a partial development of the kingdoms of nature. 

 Another system infers, on the contrary, that species are realities, and the general 

 or type idea has, in some sense, a real existence. A third admits that species are 

 essentially realities in nature, but claims that the general idea exists only as a 

 result of logical induction. 



The discussion in the preceding pages sustains most nearly the last view, that 

 species are realities in the system of nature while manifest to us only in individuals ; 

 that is, they are so far real, that the idea for each is definite, even of mathematical 

 strictness, (although not thus precise in our limited view,) it proceeding from the 

 mathematical and infinite basis of nature. They are the units fixed in the plan of 

 creation; and individuals are the material expressions of those ideal units. 



At the same time we learn, that while species aie realities in a most important 

 and fundamental sense, no comprehensive type-idea of a species can be represented 

 in any material or immaterial existence. For while a species has its constants, it 

 has also its variables, each variable becoming a constant so far only as its law and 

 limits of variation are fixed ; and in the organic kingdoms, moreover, each 

 individual has its historic phases, from the germ through the cycle of growth. The 

 general idea sought out by induction, therefore, is not made up of invariables. Li- 

 mited to these, it represents no object, class of objects, or law, in nature. The 

 variables are a necessary complement to the invariables ; and the complete species 

 idea is present to the mind, only when the image in view is seen to ba ever 

 changing along the lines of variables and developement. "Whatever indidualized 

 conception is entertained, it is evidently a conception of the species in one of its 

 phases, — that is, under some one specific conditon as to size, form, color, constitu- 

 tion, &c., as regards each part in the structure, from among the many variations in 

 all these respects that ai'e possible : mind can picture to itself individuals only and 

 not" species, and one phase at a time in the life of an organic individual, not the 

 whole cycle. 



We may attempt to reach what is called the typical form of a species, in order 

 to make this the subject of a conception. But even within the closest range of 

 what may be taken as typical characters, there are still variables ; and moreover, 

 we repeat it, no one form, typical though we consider it, can be a full expression of 

 the species, as long as variables are such an essential part of its idea as constants 



