CHASTER : SPECIES AND VARIATION. '2.^ 



found. But in some localities, fide Gwyn Jeffreys, all intermediate 

 forms occur. Here we are confronted by a new problem : — Are we 

 to rank these two mollusks as species or as varieties ? Perhaps the 

 simplest and most accurate answer is to say that they are two species 

 usually but in certain localities a species and a variety only. Such 

 apparent paradoxes must of necessity occur if we are to attempt to be 

 absolutely accurate. In the study of the living beings that surround 

 us we are dealing with objects that are constantly undergoing 

 change ; what to-day is a mere trifling variety may in the course of 

 time become more and more strongly characterised, whilst the type form 

 remains more or less stationary or alters in quite another direction. 

 Obviously it is impossible to say with precision that the exact stage 

 has been reached when two forms become worthy of separation. No 

 two observers would ever agree upon all cases. The most accurate 

 meteorologist could never say of a changing cloud that at one second 

 it was cirrus and the next cumulus. Even if he adopts the inter- 

 mediate cirro-cumulus accurate delimitation is rendered no more 

 easy. 



Nature never works by processes capable of complete expression 

 in the arbitrary standards we set up. iVnd all our standards are 

 arbitrary. We have no knowledge of an absolute zero of temperature. 

 Atomic weights are only comparative. Our units of weights and 

 measures are purely arbitrary, and so on. And we must perforce 

 recognize the fact that the term species is one which is capable 

 neither of exact definition nor of exact application. 



It is merely the name we give to a group of animals or plants 

 which is sufficiently different from other groups as to be worthy of 

 a separate designation by which we may refer to that group. It is a 

 term of convenience to facilitate the interchange of ideas between 

 workers. 



Hence we must recognize the fact that different students will never 

 agree upon the vexed subject of the validity of specific distinctions ; 

 one will be impressed by the marked differences between two forms ; 

 another, having made a series of different observations, will be struck 

 by the occurrence of connecting links that make him uncertain as to 

 whether he can effect a reasonable sep.aration. Consequently we 

 are always being impressed by the diversity that is observable in 

 the valuation of the term species by different students or schools of 

 students of the same group. We constantly refer to the hair-splitting 

 propensities of our Continental co-workers. They in turn will doubt- 

 less consider that we are in a measure unobservant and fail to 

 recognize differences unless they are very conspicuous. It cannot 

 be said that one is right and the other wrong, each is acting in 

 perfect accordance with his standard ideas : the only point that is 



