1889.] 



THE YOUNG NATURALIST. 



99 



complex as they are variable. We have first the weather, then the 

 effect of other animal life, then the influence of plant life, and these 

 three so interact, are so mutually dependent and contingent, that we 

 could never in our present state of knowledge define the real deter- 

 mining cause of any particular so called natural result. 



My idea then is that there are emergences every year of such 

 insects as we are considering in all the places where they are ever 

 found, and that every year an infinitely greater number of ova are 

 laid than ever reach maturity, but that by some conjunction of 

 circumstances which we do not at present accurately know, the ova, 

 larvae, or pupae, or all three were, say in the case of Galii, during 1887, 

 peculiary exempt from those adverse influences which unusually 

 decimate them, that this led to a relatively large emergence this last 

 summer and through some still further favourable influences to a very 

 large number of mature larvae. Next year such influences may have 

 ceased to act or others arise which may neutralize them, and but few 

 successors may escape to carry on the line till the next favourable 

 season. And I fancy if we had any idea of the infinite number of 

 contingencies which went to make up such favourable seasons, we 

 should not feel surprised that they occur so seldom. 



The subject could be greatly elaborated in a larger paper, but I 

 have only wished to suggest the line which I think an explanation of 

 these phenomena will take. 



I do not quite deny the possibility of other and perhaps even less 

 known reasons. I sometimes fancy that there is such a thing as 

 irregular fertility of parents during successive seasons, caused perhaps 

 by climatic or other conditions, that in certain years far more ova are 

 deposited than in others per imago, but of course this is merely 

 unsupported hypothesis. Nature does not too readily yield up her 

 secrets, and when we can explain why damson trees which in this 

 part of the country bear usually but an indifferent crop, should once 

 in ten years or so, be almost borne to the ground over a whole country 

 side with exceptional abundance, without the slightest traceable 

 reason, then we may be able to understand a little better than at 

 present why Edtisa should have swarmed everywhere in 1877, an( ^ 

 Galii in its own particular haunts in 1888. 



Hallwood, Ledsham. 



