The Origin of the Markings of Caterpillars. 363 



all the species of the group they are the goal 

 towards which the phyletic force is urging, and 

 which must sooner or later be reached by each 

 member of the group. On the other hand, I 

 cannot express so decidedly my own opinion, viz., 

 that such complicated characters as the many- 

 coloured oblique stripes or eye-spots are never 

 the results of purely internal forces, but always 

 arise by the action of natural selection, /. e. by the 

 combination of such minute and simple variations 

 as may present themselves. It may be replied 

 that the formation of eye-spots in those species 

 which are at present devoid of them, cannot indeed 

 be considered impossible, but that they would 

 only appear if the constitution of these species 

 had a tendency to give rise to the production of 

 darker spots on the edge of the subdorsal line, 

 and if, at the same time, the possession of eye- 

 spots would be of use to the caterpillar under its 

 special conditions of life. 



The condition of affairs would be quite different 

 if we were simply concerned with the transference 

 of a character from one segment on which it was 

 already present, to the remaining segments. The 

 transference would, in this case, result from causes 

 purely innate in the organism from the action of 

 laws of equilibration or of growth (correlation), and 

 the external conditions of life would play only a ne- 

 gative part, since they might prevent tire complete 

 reproduction of a character such, for example, as 



