RECENT EXPERIMENTS IN HYBRIDISATION. 193 



1. The freshly-hatched larva closely resembles the female 

 parent. 



2. With the process of growth a resemblance to the male 

 parent gradually increases. 



3. The final extent of approximation towards the male 

 parent depends on the relative phylogenetic age of the two 

 species ; the older being able to transmit its properties, whether 

 of structure or habit, better than the younger. 



Thus the crossing of S. pavonia S with the phylo- 

 genetically younger S. pyri ? gives rise to a larva in which 

 at first the maternal and afterwards the paternal characters 

 predominate. 1 The resulting perfect insect is by more 

 than two-thirds of its external appearance 5. pavonia, and 

 by less than one-third S. pyri. Its habits and functions 

 correspond with its external aspect. It prefers to fly by 

 day, like .S. pavonia 6, and pairs easily with the female of 

 that species, from 43 to 62 per cent, of the eggs being fer- 

 tile. On the other hand, it does not pair readily with S. 

 pyri, and the resulting eggs on an average of nine cases gave 

 only one larva from 180. 



Similarly 5. pavonia S, when paired with the phylo- 

 genetically older .S. spini ? , gives a form of which in the 

 perfect state about two-thirds of the external aspect belong 

 to the type of 5. spini. The male flies by night. After 

 crossing with S. pavonia ? the resulting eggs were only 

 fertile to the extent of 16 to 22 per cent.; while the crossing 

 with S. spini ? , though not easily brought about in con- 

 sequence of their diverse times of appearance, yielded eggs 

 of which from 94 to 98 per cent, were fertile. 



Thus the male .S. pavonia is able to influence the issue 

 of the relatively gigantic 5*. pyri ? much more than that of 

 ►S". spini ? . 



Again, the issue of S. spini cf and S. pavonia ? is much 

 nearer 5". spini than is that of S. pavonia $ and .S. spini ? . 

 Hence, 



4. In reciprocal pairing the male is able to transmit the 

 characters of the species in a higher degree than the female. 



1 Barrett {Joe. cit., p. 11) says, quoting Porritt, that the larvae of the 

 cross between Smerinthus ocellatus and S. populi, "though like those of 

 S. populi when young, appear to become intermediate, or even to re- 

 semble those of .S. ocellatus when full grown ". 



