LÉPIDOPTÉROLOGIE COAIPARÉE 4/1 



that both they and the parent form hâve persisted, what has so 

 separated them that each is entitled to the lank of a species 

 becomes the next question. Along vvith a différence in the appea- 

 rance of the new form there would axise a pliysiological différence, 

 becoming more and more pronounced, which, in the end, would 

 teanifest itself as a slight but growing sterility in the actual 

 crossings between the two forms, and ûnally, from an inability 

 to combine the physiological chaiacters of the parents, an almost 

 total sterility of the products. 



An example of the former, combmed with a distinct disincli- 

 nation to pair at ail, is seen m the case of typical Piens napi 

 and its Alpine variety bryoniœ. 



If thèse assumptions are true, then the degree of the sterility 

 of the progeny of various crossmgs would be a certain test of the 

 physiological divergence of the parents, and if we can obtain 

 corroborating proofs of this divergence from other sources, we 

 are thus ablc to prove mdirectly that our spéculations as to the 

 origin of species are, to say the least, justified. What facts do 

 our experiments yieid us ? We hâve seen that the hybrids between 

 Pœcilopsis and Lycia are reasonably fertile, whilst those pro- 

 duced either by crossing Pœcilopsis and Ithysia, or Lycia and 

 Ithysia are practically stérile. 



And this sterility is not a resuit of gynandromorphism in 

 either sex, for an anatomical examination by means of the 

 microscope, shows that the génital organs in both sexes are per- 

 fectly formed. In other words, the sterility is due to a failure 

 to blend in order to form germs functionally active in the hybrid 

 individual. We are thus driven to the conclusion that Lycia and 

 Pœcilopsis are separated by a short period in respect to their 

 existence as gênera, whereas Lycia has been separated a long 

 time from Ithysia and so has Pœcilopsis, facts easily obtained 

 otherwise from a study of the structure of the larvae or, indepen- 

 dently, form the genetic séquence of the colouring of the imagines 

 for we hâve, passing from ItJiysia (as typiâed by /. zonaria) 



