468 LÉPIDOPTÉROLOGIE COMPARÉE 



4. Independent of the last point, the greater influence of the 

 maie in determining the appearance of the hybrids. 



5. The distaste of the hybrid larvae for such food plants as 

 yarrow {Achillea millefolium), l'rifolium, etc., that is to say, 

 the food plants of the Ithysia group. 



6. The failure to yield females observed in certain crossings. 



7. The gynandromorphic nature of certain of the secondary 

 hybrids. 



A. Strength of the larvae and the sterility of the crosses. 



The first two points are taken together, not because they are 

 intimately connected, but because of the light the two combined 

 throw on the origin and fixation of species. The experiments 

 described above, differ from most of those of other observers in 

 as much as, whilst they dealt with species very close to one another 

 as regards strength, in this group, many of the crosses were 

 between parents differing enormously in this respect. For 

 instance, the members of the genus Ithysia are exceedingly tender, 

 and die for no apparent reason under conditions in which the 

 members of the gênera Lycia and Pa cilopsis, with the possible 

 exception of the species lapponaria, continue in robust health. 



This is not confined to artificial conditions, for /. zonaria 

 shows the same weakness in a state of nature, and very many 

 larvae die just when full grown. 



In my case it lias been the universal resuit that, in ail cases 

 where crosses were made between an individual chosen from the 

 hardier gênera and one from the Ithysia group, instead of the 

 hybrid larvae being as weak as the weaker member, or as one 

 might expect from their hybrid origin, weaker than it is, they 

 were as strong as the stronger parent. In other words, strength 

 is dominant. Not only is this so, but when one crosses lapponaria 

 and zonaria, neither of which is conspicuous for its strength, 

 although in my expérience lapponaria is the stronger, the vigour 

 of the larvae seems to be cumulative, that is to say, the hybrid 



