The Origin of the Markings of Caterpillars. 173 



search for new forms, there is another field which 

 maybe successfully worked, viz., the precise inves- 

 tigation of the development of known species. 



The first portion of the present essay consists 

 of the determination of this development in those 

 species of Sphingidce which have been accessible 

 to me. Seven genera are successively treated of, 

 some completely, and others only in some of their 

 stages ; and thus I have sought to present a picture 

 of the course of development of the markings in 

 each genus, by comparing the species with each 

 other, and with allied forms in cases where the 

 young stages were unknown. In this portion, as 

 far as possible, the facts only have been given, the 

 working up of the latter into general conclusions 

 upon the development of marking being reserved 

 for the second portion. A complete separation of 

 facts from generalizations could not, however, be 

 carried out ; it appeared convenient to close the 

 account of each genus with a summary of the 

 results obtained from the various species. 



After having established that the markings of 

 the Sphinx-caterpillars had undergone an ex- 

 tremely gradual phyletic development, conform- 

 able to law, in certain fixed directions, it appeared 

 desirable to investigate the causes of the first 

 appearance of these markings, as well as of their 

 subsequent development. The question as to the 

 biological significance of marking here presented 

 itself in the first place for solution, and the third 



