380 Thoughts on Species. 



nence of species, tlieir mutability or immutability; and at the 

 same time, in order tliat 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 conceptions 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 uftity of type ; and 

 this general notion, when written out in words, we may take as 

 an approximate formula of the species. One system of philoso- 

 phy tlience argues that this result of induction is nothing but a 

 notion of the mind, and that species are but an imaginary pro- 

 duct 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 reali- 

 ties 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 mate- 

 rial expressions of those ideal units. 



At the same time, we learn, that while species are realities in a 

 , most important and fundamental sense, no comprehensive type- 

 idea of a species can be represented in any material or immate- 

 rial 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 king- 

 doms, 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- 



