354 Studies in the Theory of Descent. 



The only escape from this difficulty is perhaps 

 to be found in proving that D. Hippophaes for- 

 merly possessed ring-spots, and that these have been 

 subsequently either partially or completely lost, so 

 that their occasional appearance in this species 

 would therefore depend upon reversion. The 

 ontogeny, however, teaches us that this is not the 

 case, since the young caterpillar does not possess 

 a greater number of more distinct ring-spots, but 

 wants them altogether with the exception of a red 

 spot on the eleventh segment, which is, however, 

 much fainter than in the last stage. 



This last-mentioned fact contains the solution 

 of the problem. The premises from which this 

 reasoning set out were all incorrect the one red 

 spot on the eleventh segment is likewise a ring- 

 spot, and indeed the most important one of all, 

 being primary, or the first to come into existence. 

 Now all specimens, without exception, possess this 

 first ring-spot, which is useful, and has therefore 

 been called forth by natural selection ; it is not 

 inherited, but newly acquired by this species ; at 

 least, if the explanation of these spots which I 

 have previously offered is correct. 



The primary pair of spots may have been trans- 

 ferred from this to later species by heredity ; and 

 since, in all segmented animals there is a tendency 

 for the peculiarities of one segment to be repeated 

 on the others, this repetition must have occurred 

 with greater frequency and more completely in 



