•^46 Letters, Extracts, and Notes. [Ibis, 



sceptical on the point as to whether Natural Selection, 

 acting on even discontinuous variations, can have any 

 practical effect on the formation of species, or whether 

 it is not superfluous to invoke the action of Natural 

 Selection at all — nor do we believe in the action of en- 

 vironment in the initiation of new species. The only thing 

 in our opinion which can give rise to a new species is the 

 conjugation of two gametes possessed of some unusual 

 factor or other to form a zygote. We believe that the 

 beginnings of a new species may occur from the union 

 of any two birds anywhere, and is a matter of the chance 

 presence or absence, stimulation or suppression, of factors 

 in the germ-plasm. It must be remembered, however, that 

 over so small a part of the world's history do man's obser- 

 vations extend in point of time, that we cannot definitely 

 state whether or not species are being formed at all at the 

 present day. 



There is, moreover, a point in this question of the value 

 of subspecies to which we cannot help thinking ornitholo- 

 gists in general have not hitherto paid sufficient attention. 

 They appear, indeed, to have ignored the very probable fact 

 that there are two main forms of variations — one known as 

 '^mutational," in which the variation is discontinuous and 

 dependent on the presence in the organism of definite 

 factors which are resident in the (jerni-plasm, and iv/iich are 

 therefore heritable, the other known as a " fluctuatioual," 

 " environmental," or continlious variation, which is directly 

 due to the action of the environment on the soma during 

 the lifetime of the organism, and which effect cannot be 

 passed on to future generations. 



We think there can be little doubt that many — indeed, by 

 far the majority — of our present-day subspecific forms belong 

 to this last category, and are mere environmental, unstable, 

 and essentially superficial variations, which would quickly 

 disappear if the organism were transferred from its normal 

 environment to some other of a different nature. Many 

 such environmental subspecies present variations which are 



