74 



THE AMEBIC AN NATURALIST [Vol. XLII 



tion lets them slip," or rather leaves them behind in the 

 process of modification. The peculiarities of the par- 

 ents in an isolated group become intensified by in and in 

 breeding. They become modified in a continuous direc- 

 tion by the selection induced by the local environment. 

 They are possibly changed in one way or another by 

 germinal reactions from impact of environment. At last 

 a new form is recognizable. And this new form is never 

 coincident in its range with the parent species, or with 

 any other closely cognate form, neither is it likely to be 

 in some remote part of the earth. Whenever the range 

 of two such forms overlaps in any degree, the fact seems 

 to find an explanation in reinvasion on the part of one 

 or both of the forms. The obvious immediate element 

 in the formation of species is, therefore, isolation, and 

 behind these are the factors of heredity, of variation, of 

 selection, and others as yet more or less hypothetical in- 

 volved in the effect of impact of environment on the germ 

 cells themselves. The formation of breeds of sheep as 

 noted by Jordan and Kellogg (p. 82), seems exactly par- 

 allel with the formation of species in nature. In like man- 

 ner, the occasional development of breeds arising from the 

 peculiarities of individuals is possibly parallel with the 

 " mutations" of the evening primrose. Such breeds are 

 the Ancon sheep in Connecticut and the blue-cap Wensley- 

 dale 1 sheep in Australia. The ontogenetic species— 

 groups in which many individuals are simultaneously 

 modified in the same way by like conditions of food or 

 climate— show no permanence in heredity. Such forms, 

 however strongly marked, should, therefore, have no per- 

 manent place in taxonomy. The recent studies of Mr. 

 Beebe on the effects of moist air in giving dusky colors 

 to birds serve to illustrate the impermanence of the groups 

 or subspecies characterized by dark shades of color de- 

 veloped in regions of heavy rainfall. 



It may also be noted in passing that one cause of the 



'Blue Cap, a ram of Leicester-Teeswater parentage, having a blue 

 known as the Wensleydale, in Australia. 



