The Origin of the Markings of Caterpillars. 355 



the later species the more so if the process were 

 favoured by natural selection, i.e. if the row of 

 ring-spots which originated in this manner could 

 in any way be turned to the use of the species. 



\i\Hippophaes itself there must also be a ten- 

 dency to the formation of secondary ring-spots, 

 and indeed in a number of specimens we actually 

 see series of such ring-spots, the latter being pre- 

 sent in varying numbers, and in very different 

 states of development. The fact that the ring- 

 spots have not become a constant and well- 

 developed character, is simply explained by the 

 circumstance that as such they would have endan- 

 gered the existence of the species. 



In this case there is therefore no necessity for 

 assuming a phyletic vital force. The ring-spots 

 of the genus Deilephila rather furnish us with an 

 excellent explanation of a fact which might other- 

 wise have been adduced in support of a phyletic 

 vital force, viz., the strict uniformity in the develop- 

 ment of larval markings. 



Before I had been led to the discovery, by the 

 study of the marking and development of Hippo- 

 pha'e's, that the spots of the genus Deilephila origin- 

 ated on one segment only, from which they were 

 transferred secondarily to the others, this astonish- 

 ing regularity appeared to me an incomprehensible 

 problem, which could only be solved by assuming 

 a phyletic vital force. If it be attempted, for the 

 ten species here considered, to construct a gqnea- 



A a 2 



