The Origin of the Markings of Caterpillars. 353 



any ring-spots as its only marking. If D. Hippo- 

 phaes were thus marked, there would be no objec- 

 tion to the theoretica lassumption that this * was the 

 ancestor of the other species. It would then be 

 said that ring-spots were first developed in a later 

 species by natural selection, and that they had been 

 transmitted to all succeeding and younger species. 

 Certain individuals of D. Hippophaes, however, 

 possess small ring-spots, some of which are well 

 developed on several segments. In this species 

 the row of ring-spots is therefore comprised in the 

 development. The remaining species, which are 

 much younger phyletically than Hippophaes, could 

 not have inherited their ring-spots from the latter, 

 since this species itself only possesses them occa- 

 sionally, and, so to speak, in a tentative manner. 

 The spots would therefore appear to have arisen 

 spontaneously in this species, and independently 

 of those in the other species. But if this were the 

 case, how should we be able to prove that in the 

 other species also the ring-spots did not arise 

 independently ; and if, moreover, a large number 

 of species showed the same character without its 

 being referable to inheritance from a common 

 ancestor, how could this be otherwise explained 

 than as the result of a force innate in these species 

 and producing similar variations ? But this is 

 nothing bnt Askenasy's " fixed direction of varia- 

 tion" i.e., a phyletic vital force. 



1 Or some other extinct analogously-marked species. 



A a 



