The Origin of the Markings of Caterpillars. 287 



principles and compelling us to admit the exist- 

 ence of a force of development innate in the 

 organism. In any case the " phyletic vital force " 

 can only be got rid of by a process of elimination 

 by proving that all the characters generally oc- 

 curring throughout the group of phenomena in 

 question, must be attributed to other causes, and 

 that consequently nothing remains for the action 

 of the supposed phyletic vital force, which 

 would in this manner be negatived, since we 

 cannot infer the presence of a force if the latter 

 exerts no action whatever. 



I shall here attempt such an investigation of the 

 group of phenomena displayed by larval markings, 

 with special reference to those of the Spkingidte. 

 The alternatives upon which we have to decide 

 are the following : Are the markings of cater- 

 pillars purely morphological characters, produced 

 entirely by internal causes ? or, are they simply 

 the response of the organism to external influ- 

 ences ? 



The solution of these questions will be arrived at 

 by seeking to refer all the markings present to 

 one of the known transforming factors, and the 

 success or failure of this attempt will give the re- 

 quired decision. The first question to be attacked 

 is obviously this, whether the Sphinx-mark- 

 ings are actually, as they appear at first sight, 

 purely morphological characters. If it can be 

 shown that all these markings were originally of 



