360 St^ld^es in the Theory of Descent. 



have here the proof that such spots first arose in a 

 precisely similar manner in several species, quite in- 

 dependently of one another that, in fact, a " nxed 

 direction of variation " in a certain sense exists. 



In three species of Smerinthus~\a,rv<\ red spots 

 appear towards the end of the ontogeny ; in S. 

 Populi and Ocellatus in only a minority of indi- 

 viduals, and always separate (not coalescent), 

 and in . Tilicz in a majority of specimens, 

 the spots frequently becoming fused into one 

 large, single, longish marking. These three 

 species cannot have inherited the spots from a 

 common ancestor, since they are absent in the 

 younger ontogenetic stages, or occur only excep- 

 tionally, becoming larger and more numerous in 

 the last stage ; they obviously form a character 

 which must be considered as a case of " anticipated 

 development." 



How is it then that three species vary inde- 

 pendently of each other in an analogous manner ? 

 I know of no other answer to this question than 

 that similar variations must necessarily arise from 

 similar physical constitutions or, otherwise ex- 

 pressed, the three species have inherited from an 

 unknown parent species, devoid of spots, not this 

 last character itself, but a physical constitution, 

 having a tendency to the formation of red spots 

 on the skin. 3 The case offers many analogies to 



3 [Compare this with Darwin's remarks on "analogous 

 variations," "Origin of Species," 6th ed., p. 125. R.M.] 



