1889.] 



THE YOUNG NATURALIST. 



to dogmatize upon, and secondly that if they were, they would not 

 have that importance which he attaches to them. As I understand 

 him he reasons thus : — 



1. Continental naturally-bred specimens average nearly half-an- 

 inch more in wing expanse than English specimens bred in captivity 

 do. 



2. English caught imagines approach much more nearly to the 

 Continental type than to their own, presumably degenerate offspring, 

 therefore (i) the caught imagines must be of Continental birth ; and 

 (2) the effect of English food and climate is degeneration. 



Now leaving out of account the question of the effect of artificial 

 nurture and forcing, it strikes me that we have not nearly enough 

 caught British imagines to found any safe conclusions upon. Can 

 fifty guaranteed British (1888) caught imagines be produced for 

 measurement, and are we safe to draw any general conclusions from 

 so small a number. 



But if it could be indeed established that the descendents of the 

 insects of 1888 averaged in wing expanse considerably less than their 

 parents, might we not explain the fact in another way than by 

 attributing it to a difference of stock or of climate. A difference of 

 season might have some effect. The summer of 1888 was admittedly 

 one of maximum emergences, that is to say the occult influences, 

 whatever they may have been of 1887 were greatly in favour of healthy 

 larval life. Surely the same influences which led to a great number 

 of survivals, would lead also to the greatest well-being, the utmost 

 vigour, among those survivals, and, consequently, we might expect 

 the emergences from such larvae to exhibit in the imago form the 

 characteristics of their larval life. 



•Again, we believe the next season to have been one of waning 

 power and vigour. No doubt, and this is a point that must not be lost 

 sight of, the actual number of larvae at large during the autumn of 1888 

 was infinitely greater than during the autumn of 1887, but we fully 

 believe that the proportion of oval, larval, and pupal survivals to have 

 been less ; in short, adverse influences were at work ; the species hav- 

 ing reached its maximum was, and is now, on the wane towards its 

 minimum, and consequently we might expect this decreasing healthi- 

 ness and vigour to be apparent in individuals no less than in the race 

 as a whole. This, however, is merely a suggestion, and may be quite 

 worthless, for as I said before, I do not consider the decrease in size 

 of the bred specimens so fully proven as to force one to the convic- 

 tion that the larger parents must have been of foreign origin. 



