locauze:d stagevS in de:vkIvOpme:nt. 167 



throw any light upon the subject. These localized stages in the development 

 of the color pattern of Leptinotarsa are of value phylo genetically only as 

 indicating a similarity of constitution and organization between species. 

 That each stage represents the repeated color pattern of some ancestor is 

 a view not in accordance with the conditions shown to exist in this genus of 

 beetles. 



I have interpreted these localized stages on the basis of similarity of orig- 

 inal constitution and modification in development. The successive stages in 

 Leptinotarsa are not, however, simpler conditions, but more specialized. They 

 are not comparable to the condition found by Shull in Sium, where the local- 

 ized stages are simpler states ; although in both cases the explanation is phys- 

 iological and developmental and not phylogenetic. 



In Leptinotarsa each species, as far as we can discover, starts in larval 

 development endowed with a definite system of color-enzyme producing cells; 

 that is, all start alike from a racial condition. Given this racial endoivment, 

 each species from the start modifies, holds in check, or increases the activities 

 of the centers in its own manner, without any dependence upon the actions of 

 its immediate parental or grandparental species. In the evolution of the color 

 pattern, in the rise of new species, each species inherits this general racial 

 system of coloration entire in its germ plasm, and the fundaments thereof 

 appear in development. In the production of the neiv race the capacity to 

 modify this general color scheme is inherent in the germ plasm, and in hered- 

 ity is transmitted to the offspring of the same kind as in the parent; but in the 

 new race it is changed, the modified capacity producing new developments of 

 the color centers which we recognize as the differentials of the new races 

 or species. 



I am convinced that in these beetles at least the apparent localized stages in 

 ontogeny are nothing more than the physiological expression of similarities 

 in constitution and in developmental tendencies. 



Likewise the stages in development found in the imaginal color pattern are 

 best and most logically explained in this manner. Ancestry exerts its influ- 

 ence only by providing a general racial or generic background out of which 

 each species takes characters and variously modifies them as its specific con- 

 stitution demands, to create its color pattern in the different stages of its 

 ontogeny. Each species, however, is absolutely dependent upon this ancestral 

 background for its characters, and can not, under any conceivable conditions, 

 develop traits or characters which are not based upon some trait or character 

 existing in the ancestral background. 



