4 



nent) as a specific one ; and hence I gather the informa- 

 tion that a reviewal of our first principles is occasionally 

 necessary, if we would not restrict (however gradual and 

 imperceptibly) that legitimate freedom which Nature 

 has had chalked out for her to sport in, or strive to im- 

 pose laws of limitation in one department which we do 

 not admit to be coercive in another. 



Perhaps, however, before entering on the subject- 

 matter of this treatise, my definition of the terms 

 " species " and " variety," so far at least as such is 

 practicable, will be expected of me. I may state, there- 

 fore, that I consider the former to involve that ideal re- 

 lationship amongst all its members which the descent 

 from a common parent can alone convey : whilst the 

 latter should be restricted, unless I am mistaken, to 

 those various aberrations from their peculiar type which 

 are sufficiently constant and isolated in their general 

 character to appear, at first sight, to be distinct from it. 



The first of these enunciations, it will be perceived, 

 takes for granted the acceptance of a dogma which I 

 am folly aware is open to much controversy and doubt, 

 namely, that of " specific centres of creation." With- 

 out, therefore, examining the evidences of that theory 

 which would be out of place in these pages (and which has 

 been so ably done already by the late Professor Edward 

 Forbes), I would merely suggest that the admission of it 

 is almost necessary, in order to convey to our minds any 

 definite notion of the word " species " at all : and that, 

 hence, whilst I would not wish to reject the hypothesis 



