VARIATIONS IN ANIMALS AND PLANTS 49* 



g. General color blackish, brown or yellowish — not indigo blue. 

 /;. Color brownish, the middle of the front of body yellowish; 

 fins all yellow except the ventral, which are black. 



Accensus. 

 hh. Color yellowish pink; caudal and pectorals pale; ventrals 

 and anal bright light blue. Aflinis. 



gg. Color of body black with violet shades. 



i. Pectoral and caudal fins abruptly bright yellow. Chlorurus. 



ii. Pectoral and caudal fins violet black like the rest of the 



body. Nigricans. 



j. General color deep indigo blue everywhere on body and 



fins; body with 4 to 6 broad cross bars of darker 



blue. 



k. Cheeks plain, without distinct stripes. Indigo. 



kk. Cheeks with a dark-blue suborbital band between 



2 bands of clear blue. Bovinus. 



What the significance of this extraordinary condition may be, is 

 entirely unknown, nor do we know the determinant causes of dichroma- 

 tism. It is sufficient for the purposes of this paper to refer to the 

 fact. 



Ontogenetic Variations 



A vast range of variations are ontogenetic, or dependent on in- 

 fluences affecting directly the life of the individual. These are not 

 hereditary in the judgment of the present writer, and therefore they are 

 not direct factors in the formation of species. Many investigators take 

 a different view, believing in the direct inheritance of acquired char- 

 acters, or of the effects of environmental or functional conditions, the 

 familiar tenets of ' Xeo-Lamarckism ' or progressive heredity. 



These ontogenetic variations are, strictly speaking, individual, ap- 

 pearing as collective only when many individuals have been sub- 

 jected to the same conditions. They may be divided into environ- 

 mental variations and functional variations, two categories which can 

 not always be clearly separated, as variations due to food conditions 

 partake of the nature of both. 



In the epoch-making paper quoted above, and in other publications, 

 Dr. Allen shows that climatic influences affect the averages in meas- 

 urements and in color among birds. For example, in several species 

 of birds, the total length is greater in specimens from the north, while 

 the bills and toes are actually longer in southern specimens. That 

 this condition is due to the influence of climate on development is 

 shown by the fact that numerous species are affected in the same way. 

 It is noticed also that specimens from the northeast and the northwest 

 of the United States are darker in color than those from the interior, 

 and again that red shades are more common in the arid southwest. 

 Similar effects have been recently shown by a study of species of wasps. 

 They may be produced at will by subjecting the larva? and pupse of 



