382 PHYSICAL CONDITIONS IN GENESIS OF SPECIES. 



the warmer latitncles, occurs more rarely than in nuunmals, ahhough 

 several well-marked instances are known. The increase is generally 

 northward and is often very strongly marked. The greatest dif- 

 ference between northern and southern races occurs, as in mammals, 

 in the species whose breeding stations embrace a wide range of lati- 

 tude. In species which breed from northern New England to Flor- 

 ida the southern forms are not only smaller, but are also quite diifer- 

 ent in color and in other features. This is eminently the case in the 

 common quail {Ort{/,v rirginianvti)^ the meadow^ lark (SturneUa 

 magna), the purple grackle {Quiscalus purpureu.s), the red-winged 

 blackbird {Agelams phmniceus), the golden-winged woodpecker 

 {Colaptes a>i7ntus), the towhee {Pipilo eri/tliroplitJiaJmn.s) , the Caro- 

 lina dove {Zetuvdmxt carolhieiisis) , and in numerous other species, 

 and is quite appreciable in the blue jay {Cyanurus crhtatuH)^ the 

 crow {Corvus aniej'icanus), in most of the woodpeckers, in the tit- 

 mice, numerous sparrows, and several thrushes and warblers, the 

 variation often amounting to from 10 to 15 per cent of ihe average 

 size of the species." 



As a general rule certain parts of the organisms vary more than 

 does general size, there l)eing a marked tendency to enlargement of 

 peripheral parts under high temperature or toward the Tropics; 

 hence southward in North America. This is more readily seen in birds 

 than in mammals, in consequence mainly of their peculiar type of 

 structure. In mammals it is manifested occasionally in the size of 

 the ears and feet and in the horns of bovines, but especially and more 

 generally in the pelage. At the northward, in individuals of the same 

 species, the hairs are longer and softer, the under fur more abundant, 

 and the ears and the soles of the feet better clothed. This is not only 

 true of individuals of the same species, but of northern species col- 

 lectively, as compared with their nearest southern allies. Southern 

 individuals retain permanently in many cases the sparsely clothed 

 ears and the naked soles that characterize northern individuals only 

 in summer, as is notably the case among the ditferent s(iuirrels and 

 spermophiles. 



In mammals which have the external ear largely developed, as the 

 wolves, foxes, some of the deer, and especially the hares, the larger 

 size of this organ in southern as compared with northern individuals 

 of the same species is often strikingly apparent. It is more especially 

 marked, however, in sjiecies inhal)iting extensive open plains and 

 semidesert regions. The little wood hare, or gray "rabbit" {Lepust 



a The uiodern equivalents of several of the technical names in this paragraph 

 are as follows: Orty.r [ = CoUhhh] vU-uhiknuix ; Quhcalus imri)ureu8 [—quis- 

 cula'] ; Zcno'diira curolineihsis [=Zenai(lHra iiKtcronra] : Cyauuni>< [ = Cyano- 

 cifta] cri^tata ; Corvus atitcrivaiuis [ — brachyrhijnclwn}. — Authors note, 190G. 



