LEPIDOPTEROLOGIE COMPAREE 



469 



larv^ are very much more robust than those of either parent. Let 

 us consider the effects of this law in the case of species in natural 

 conditions. Suppose a species to develop, as a chance aberration, 

 a form somewhat more vigorous than itself either in the larval 

 or in any other stage. It is clear that a pairing between the 

 type and the aberration would resuit (granting that strength is 

 dominant), in offspring much more vigorous than the type of 

 the species and, therefore, more hkely to provide the parents of 

 the next génération. It is but f air to assume that, accompanying 

 the acquisition of the strength of the aberration, we hâve a repro- 

 duction of its outward appearance. The yield of imagines 

 resembling the new form would, in many cases, be small, but if, 

 as has been assumed, the strength of the aberration and its other 

 features are Mendelian dominants, 100 per cent of the progeny 

 would, to the eye, be departures from the typical form. Thus, 

 if we Write S for the aberration and thus indicate that its strength 

 and other features are dominant and W for the type with 

 strength, etc. récessive, then the following scheme indicates the 

 resuit of a pairing between the aberration and the type, and the 

 subséquent inbreeding of the first or Fj^ génération and also of the 

 F2 and F3 générations. 



(dorainant) 



S X W (récessive) 



S W (hétérozygote with the appearance of S) 



SS 

 (extracted 

 dominant) 



F^ >- S S 



S W 



WS 



hétérozygote looking S 



Sis 



wlw 



w w 

 ww 



SIW WIS 

 I as before 



3 — >- SS SS ww ww 



(Breeds true) (Breeds true) (Breeds true) (Breeds true) 



