286 



DR. 11. GADOW ON EVOLUTION 



[Mar. 20, 



" lumpers," who, rightly allowing more amplitude of variation 

 in their conception of a species, commit the following error. They 

 think that intergrading of two species is the same as continuity 

 from one exti-eme to the other. Foi- instance, if the overlap of all 

 the available characters should occur in one and the same specimen, 

 then presumal)ly the two supposed species would be the same, 

 but not — and this is the usual procedui'e — if the overlap of the 

 charactei's occuis only in a whole number of specimens taken 

 togethei". 



The following diagram illusti'ates an important point. Let «, h, c, 

 d be 4 different characters, each of which can vary from, let us say, 

 small to large ; and let us assume that character a (for example 

 the scutellation of the foreaim) is the quickest, the most sus- 

 ceptible, to change. Let species A change towards B, and let B 

 change towards A, by gi-adually assuming the respective characters. 

 Then it will be found that the two changing seiies will overlap com- 

 pletely oi- coincide in all theii' four characters, only when all these 

 chaiacteis have airived at a medium condition, and again when they 

 all have airived at the other extreme end. The diagiam shows 

 moreover that, although the results are the same, at tlie terminus 

 and in the middle, the A and B series of evolution are different at 

 every stage. 



Small. 



Species X =a h c d 

 changing 



towards U-* 



Medium. 



Large. 



d 



c d 

 bed 

 a h c d 



d 

 d a 

 dab I 



d a b c = a b d\ 



A lias cliiuiged into a form in 



which all the characters are 

 large ; A resembling B. 



a b c d = Species B changing into, or 

 towards A. 



b c 



d\a b c 

 d a'b c 

 d a b\c 

 dab c—a bed 



Diagram illustrating the overlapping of characters. 



Species B resembles A, but is not genetically the same, since the combinations 

 dab small, or a h c medium and d small, &c. occur nowhere in the series 

 which represents the changes from A towards B. 



In this paper I have employed a great number of specific ifec. names, 

 often using trinomials, in fact as many as the greatest of "splitters " ; 

 but this has been done for the sake of convenience, for shortness 

 of expression, and having done my best to diagnose the gioups, 



