174 Studies in the Theory of Descent. 



section is devoted to this subject. If it is main- 

 tained that marking is of no importance to the life 

 of the insect, or that it is so only exceptionally, and 

 that it is in reality, as it appears to be, a character 

 of purely morphological, i. e., physiological, insig- 

 nificance, then its striking phylogenetic develop- 

 ment conformable to law cannot be explained by 

 any of the known factors of species transformation, 

 and we should have to assume the action of an 

 innate transforming power. In the present inves- 

 tigations, this subject in particular has been exten- 

 sively treated of, and not only the markings of 

 Sphinx-caterpillars, but also those of caterpillars in 

 general, have been taken into consideration. The 

 results arrived at are indeed quite opposed to this 

 assumption marking is shown to be a character 

 of extreme importance to the life of the species, 

 and the admission of a phyletic vital force must, 

 at least from the present point of view, be excluded. 

 This leads to the fifth section, in which I have at- 

 tempted to test certain objections to the admission 

 of a " phyletic vital force." The sixth section 

 finally gives a summary of the results obtained. 



I may now add a few explanations which are 

 necessary for understanding the subsequent de- 

 scriptions. It was found impossible to avoid the 

 introduction of some new technicalities for de- 

 scribing the various elements of larval markings, 

 especially as the latter had to be treated of scien- 

 tifically. I have therefore chosen the simplest 



