ON VARIATION. 23 



originated by an accident or without a determining 

 cause. The increased amount of dark pigment ob- 

 served in animals which dwell in especially humid re- 

 gions must have a corresponding cause, and it is nat- 

 urally to be supposed, of a kind the opposite of that 

 which produces the pale colors. 



I shall adduce some illustrations which show that 

 color variations in species, as well as structural varia- 

 tions in higher groups, have appeared in certain defi- 

 nite series, and observe a successional relation to each 

 other, which may or may not coincide with geograph- 

 ical conditions. The same relation is observed in the 

 order of appearance of variations on the body. 



Eimer and Weismann have shown that the grad- 

 ual modification of color markings has originated in 

 lizards and in caterpillars at the posterior end of the 

 body and has gradually extended forwards. This has 

 been discovered both by comparisons of the variations of 

 the adults, and by studies of the order of their appear- 

 ance in ontogenetic growth. Eimer shows that longi- 

 tudinal bands have been produced in some animals by 

 the confluence of spots placed in transverse series, 

 which themselves are the remains of interrupted trans- 

 verse bands. Thus he believes that the spots of the 

 leopard group of the large cats were derived from the 

 breaking up of transverse bands of the character of 

 those now possessed by the tiger. The uniform colo- 

 ration of the lion is the result of the obliteration of the 

 spots. Traces of these spots may be distinctly seen in 

 lions' cubs. 



In plants variation is said to be equally definite by 

 Henslow. He says : "In 1847 Professor J. Buckman 

 sowed the seed of the wild parsnip in the garden of 

 the Agricultural College at Cirencester. The seeds 



