Vol 'i9^ XV ] Recent Literature. 487 



distinguishes nineteen kinds of Juncos, although two of these, montanus 

 and dorsalis, regarded as species by Ridgway, are considered to be hybrids 

 by Dwight and therefore unworthy of formal recognition in his scheme. 

 In the other forms the names employed are identical in thirteen cases and 

 in three of the remaining four they differ only in being treated as subspecies 

 by Dwight and as full species by Ridgway. The other form shufeldti of 

 Ridgway is renamed couesi by Dwight on the rather questionable claim 

 that the type specimen of shufeldti is a winter straggler of oreganus. 



That Mr. Ridgway, always a " liberal " in the matter of geographic 

 races, and Dr. Dwight, a pronounced " conservative " in systematic work, 

 should come to such substantial agreement is doubly gratifying because 

 it was unexpected, and we have the satisfaction of feeling that the arrange- 

 ment of the Juncos is substantially settled. Viewed from the second stand- 

 point Dr. Dwight's paper opens up a wide field for discussion. Years ago 

 in ' Science ' Drs. C. Hart Merriam and J. A. Allen engaged in a lengthy 

 discussion on the relative values of intergradation and degree of difference 

 in the designation of species and subspecies. Whether we are any nearer 

 to a solution of the problem now than we were then or whether the determi- 

 nation of what is a subspecies and what is a species can, from the very 

 nature of the case, ever be anything but a matter of individual opinion is 

 a question. 



Dr. Dwight lays down the law that "The species is the unit; the sub- 

 species is part of the unit; and the hybrid is an individual that is part of 

 two units," and again states that: "a species has one or more intrinsic 

 characters or a combination of characters not shared by another species. 

 The characters are qualitative," while " a subspecies shares all the characters 

 of its parent species in greater or less degree. The characters are quantita- 

 tive and without a break in the continuity." 



This is all very well but would we not be quite as justified in saying that 

 the subspecies is the unit and that the species is an assemblage of subspecies 

 having certain characters in common? Furthermore how are we always 

 to distinguish between qualitative and quantitative characters? We must 

 all admit that a species in the course of evolution is derived from a sub- 

 species and we must therefore necessarily find all intermediate stages in 

 the change from quantitative to qualitative characters and in deciding 

 where to draw the line we are confronted by the same old problem which is 

 bound to bring in personal opinion. Dr. Dwight is apparently endeavoring 

 to devise a method of naming specimens from the characters which they 

 present and no doubt intentionally he discards so far as possible the geo- 

 graphic problems involved — isolation, intergradation, environment etc. 

 This it seems to the reviewer we cannot do. We are naming forms which 

 are the result of evolution and are bound to consider every factor involved. 

 We necessarily find species and subspecies differing from one another by 

 every conceivable degree of difference and no set of criteria will serve as a 

 rule by which everyone can decide which forms are species, which sub- 

 species and which are not worthy of recognition at all. We cannot solve 



