Thoughts on Sjjecies. 381 



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

 nature. The variables are a necessary complement to tbe inva- 

 riables ; and the complete species-idea is present to the mind, only 

 when the image in view is seen to be ever changing along the 

 lines of variables and development. Whatever indidualized 

 conception is entertained, it is evidently a conception of the spe- 

 cies in one of its phases, — that is, under some one specific condi- 

 tion as to size, form, color, constitution, &c., as regards each part 

 in the structure, from among the many variations in ;all these 

 respects that are possible : mind can picture to itself indivi- 

 duals 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 I'ange 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 expres- 

 sion of the species, as long as variables are such an essential 

 part of its idea as constants. The advantage of fixing upon 

 some one variety as the typical form of a species is this, — that 

 the mind may have an initial term for the laws embraced under 

 the idea of the species, or an assumed centre of radiation for its 

 variant series, so as more easily to comprehend those laws. 



Again, abrupt transitions and not indefinite shadings have 

 been shown to be the law of nature. In proceeding from special 

 characters to a general species- idea, nature gives us help through 

 her stepping stones and barriers. In former times, man looked 

 at iron and other metals from the outside only, and searching- 

 out their differences of sensible characters, gradually eliminated 

 the general notion of each, by the ordinary logical method of 

 generalization. But science now brings the element to the line 

 and plummet, and reaches a fixed number for iron and other 

 elements as to chemical combination, etc. By this means, the 

 studying out of the idea of a species seems almost to have 

 escaped from the domain of logic into that of direct trial by 

 weights and measures. It is no longer the undefined progress 

 of simple reason, with a mere notion at the end, but an a^^peal 

 to definite measurable values, with stable numbers at bottom, 

 fixed in the very foundations of the universe. So, in the or- 

 ganic kingdoms, where there is, to our limited minds, still greater 

 indefiniteness in most characters, the barrier against hybridity 



