— 5 — 



to be stable within a certain definite area", and he considers 

 "that a subspecies becomes a full species when Nature, in the 

 course of evolution, has eliminated the intervening forms." 



Hartert (Bull. Brit. Orn. Club, vol. XL, 1920, p. 87) 

 objected to make supposed intergradation between two forms the 

 criterion in the subspecies", and he thinks that "there are 

 numerous instances, in which no intergradation could be traced, 



— in fact, we seldom found it to exist". As subspecies he con- 

 siders forms which agreed in their main characters, while they 

 differed in details (either of colour, markings or dimensions) and 

 represented each other geographically — or that subspecific 

 characters where "differences combined with geographical separa- 

 tion", agreement in structure and general features, of course, 

 being established. 



B n h t e considers "that a subspecies is a form of species 

 that differs from the same species in another locality owing to 

 its environment, e. g. its geographical position" (Bull. Brit. Orn. 

 Club, vol. XL, 1920, p. 89). He also considers that when two 

 closely allied forms were found breeding in the same locality 

 they must be considered true species (that is, belonging to diffe- 

 rent "form circles".) The German ornithologist Gengler (Die 

 Balkanvogel, 1920, p. 16) sums up his opinion in the following 

 sentence: "There is no'species and no subspecies. There are only 

 "form circles", which are composed of separate, geographical 

 forms. All these geographical forms are equivalent and none 

 can be made superior or subordinate to the other", and in this 

 way the talk of species and subspecies is done away with. 



In modern Ornithology the various theories of "form- circles", 

 so meritoriously worked out by Tschusi zu Schmidhoffen, 

 Hartert, Kleinschmidt and many other eminent investi- 

 gators, differ however on one or two points. As already pointed 

 out, Hartert considers that "intermediates between two or 

 several forms by no means always exist", and Stresemann 

 (Journ. f. Orn., 1919, p. 296) also expresses the same opinion, 

 pointing out that mountain ranges often form well-defined divi- 

 ding-walls between two closely related forms. Further, connec- 

 ting-links between islandforms and those on the adjacent main- 

 land are almost always missing. But in those cases where 

 such intermediate forms are really found one can be in a doubt 

 as to how these forms are to be named. As S t r e s e m a n n (op. 

 cit.) has pointed out, it is possible to express by means of figures 



— almost as in chemical formulae — the degree of the position 

 of an intermediate form in relation to the forms between which 

 the connecting line in question is situated. Such a proceeding, 

 however, seems to me to be arbitrary and too subjective on the 

 whole to have any scientific value, and without careful genetic 

 investigations the affinity between the forms cannot, I suppose, 

 be found by means of a more or less superficial morphological 



