554 



HCIENCE. 



[N. S. Vol. XXII. No. 566. 



I know of no example under question 4. 



WALTER KENRICK FISHER. 



1. In Melospiza cinerea pusillula Ridgway and 

 M. c. santcecrncis Grinnell we have two conspecific 

 races inhabiting the same region but occupying 

 different habitats. 



2. Santoecrucis (a distinguishable but very 

 closely related race to cooperi Ridgway, of the 

 San Diegan-Los Angeles district ) , dwells in the 

 valleys and on lower mountain slopes of the Santa 

 Cruz Mt. peninsular, and as far south as southern 

 Monterey Co., California. It is common along the 

 fresh-water streams emptying into both sides of 

 the south arm of San Francisco Bay. But M. c. 

 pusillula breeds only on the marshes, among the 

 Salicornia. Its range is consequently surrounded 

 by that of M. c. santcecrucis. East of Palo 

 Alto one can stand by nests of santcecrucis and be 

 v^ithin shouting distance of many nests of pusil- 

 lula. Yet the two races never, during the breed- 

 ing season, encroach upon one another's domain. 

 ,The M. c. samuelis of Baird occupies the salt 

 marshes along the northern arms of San Fran- 

 cisco Bay. So far as known it does not inter- 

 grade with M. c. pusillula. 



3. Not if coextensive in habitat throughout a 

 large part of the range of both forms. If inter- 

 gradation was proved beyond a doubt it might be 

 shown that one race had encroached upon an- 

 other over part of its range. Intergradation has 

 been satisfactorily established in so few cases 

 that one would be justified in calling such forms 

 species. 



4. The only case I can recall is that of Empi- 

 donax hammondi and E. ivrighti, which are prac- 

 tically indistinguishable out of hand. They breed 

 commonly in the high Sierra Nevada and over 

 western North America. So far as genetic rela- 

 tionship is concerned there is a probability that 

 hammondi may be a descendant of the eastern 

 mini7nus stock, while wrighti may be nearer E. 

 fulvipectus (S. Mexico). 



I have written out the only cases I know of 

 which will bear on your questions. The song 

 sparrow case, is easily explained by a difference of 

 habitat. The word ' region ' is of course sus- 

 ceptible to many interpretations. In California 

 where zones are wonderfully juxtaposed in a sort 

 of nature's crazy-quilt one has to be unusually 

 specific as to locality. Birds labeled Santa Clara 

 Valley, for instance, would considerably mislead 

 one unacquainted with the region, if he happened 

 to receive specimens of two subspecies of song 

 sparrow. 



Referring to the land snails of the island 

 of Oahu (Hawaii), Alfred Russel Wallace 

 quotes from Rev. J. T. Gulick the state- 

 ment that the island has in its wooded por- 

 tions about 175 species of land-shells repre- 

 sented by 700 or 800 varieties. 



We frequently find a genus represented in sev- 

 eral successive valleys by allied species, sometimes 

 feeding on the same, sometimes on allied plants. 

 In every case the valleys that are nearest to each 

 other furnish the most nearly allied forms, and 

 a full set of the varieties of each species presents 

 a minute gradation of forms between the more 

 divergent types found in the more widely sepa- 

 rated localities. 



Similar conditions are recorded among" 

 the land snails in Cuba and in other re- 

 gions. In fact, on a smaller scale, the 

 development of species of land and river 

 moUusks has everywhere progressed on 

 similar lines with that of birds and fishes. 

 Many other illustrations of the same sort, 

 drawn from almost all groups of animals, 

 have been given by Dr. Moritz Wagner, 

 whose epoch-making work has not received 

 from writers on organic evolution the at- 

 tention it deserves. Perhaps one cause of 

 this neglect is found in Wagner's persistent 

 opposition to the theory of natural selection 

 and his insistence on isolation and migra- 

 tion as virtually the only factors in species 

 forming. But to recognize isolation as 

 practically a necessary condition in the 

 subdivision of species need not necessarily 

 eliminate or belittle any other factor. Iso- 

 lation is a condition, not a force. Of itself, 

 it can do nothing. Species change or di- 

 verge with space and with time ; with space, 

 because geographical extension divides the 

 stock and brings new conditions to part of 

 it; with time, because time brings always 

 new events and changes in all environment. 



One of the most remarkable cases of 

 group evolution is that of the song birds 

 of Hawaii, constituting the family of 

 Drepanida3. In this family are about 

 forty species of birds, all much alike as to 



