298 ON THE EXISTENCE OF 



take place, as to have led to the supposition that nature knows 

 no division of kinds or '' genera" but that specific distinction 

 is all that can be proved to exist. 



Now as this supposition is what I have proposed as the 

 subject of inquiry in the present paper, it may be as well, 

 before entering upon the inquiry, to give a definition of a 

 " genus ;" and in so doing, I must observe that, supposing the 

 existence of generic groups in nature, the characters by which 

 we separate such groups must necessarily be, in some measure, 

 arbitrary, since we cannot know of a certainty where one 

 group terminates, and another begins. I define a " genus" 

 to be — 



A group of specifically distinct individuals, similar to each 

 other, more or less, in habits and economy, which have at least 

 one character in common, and this a character either not found 

 in other groups, or not found in other groups with a like 

 combination of characters. 



The aphorism, " Natura non facit saltiis," is generally 

 acknowledged to be true, and of its truth I am fully convinced ; 

 for so gradual is the transition from one form to another, not 

 only in entomology, but in every form of matter throughout 

 nature, at least where we have most knowledge, that it is but 

 reasonable to suppose, when we observe any insulated form, it 

 is only so insulated because the links which would make it 

 harmonize with the whole are unknown to us. But admitting 

 this, I contend that groups do exist in nature, of which the 

 individuals of each respectively agree, more or less, in general 

 characters, one with another, but do not so agree with the 

 individuals of any other group. 



As it is to be supposed that "genera" exist throughout 

 nature, if at all, it signifies but little from which part of nature 

 we reason. Let us, therefore, for the sake of illustration, take 

 the horse, the zebra, and the ass, and place them in a group 

 together. The first thing that strikes us is, that they have a 

 great general resemblance to each other : the outline of their 

 respective forms is much the same ; their various members are 

 similar, their habits are nearly alike : in these points the three 

 individuals agree one with another. But, following up the 

 comparison, we find that, although a general resemblance 

 obtains between them, they differ from each other in certain 

 'particulars, which, as the position is all we want, may be 



