336 Mr. G. Lewis on the 



larvae can get sufficient nutriment where a larger species 

 would starve, and this is perhaps enough to account for 

 its constant size and moderate sexual differences. Even 

 in Macrodorcus, the nibrqfemoratus is more constant in 

 size than some of the others, and on the 8th June, 

 1880, I took, at Chiuzenji, fifty specimens from a single 

 beech, and into this tree my axe was easily driven four 

 or five inches by a fair blow. The larvae here could 

 penetrate the whole tree, and obtain such nutriment as 

 was necessary for normal development, and under these 

 conditions there was no conspicuous variation in the size 

 of the imagos. The Prismognathus again, which varies 

 but little, feeds in rotten birch trees, a tree which, like 

 the beech, rots quickly away, and is different in this 

 respect both to the oaks and to the tropical hard-wooded 

 trees, which only decay by inches at a time. 



The larva of a Cicindela, Carabus, or Dytiscus has the 

 power and habit of seeking food, and can generally 

 obtain what is necessary ; but wood-feeding larvae, such 

 as those of Lucanidce and Cerambycidce, the imagos of 

 which vary so much in size, are almost wholly dependent 

 on the incident of the whereabouts a certain female may 

 deposit her ova : if on or near very hard wood they are 

 starved ; if on more nutritious material they become 

 vigorous. Eoughly speaking, in a Cicindela the size is 

 constant and normal, and in a Cerambyx variable and 

 irregular. A tree-larva, while feeding and coming on a 

 hard knob or nodule, may become starved or emaciated, 

 but a ground-feeding species is not isolated in the same 

 way, and the evidence of its better position is that it 

 varies less in bulk and stature. 



It thus appears probable that when a species, 

 during a long series of generations, has lived (without 

 the exertion of finding it) amidst an abundant, but 

 occasionally variable, supply of easily assimilated food, 

 it has acquired a superior stature for its individuals, the 

 acquisition of which carries with it a capacity of special 

 sexual development. And at the same time the species 

 obtains to a greater plasticity than in other kinds, 

 which enables it under less favourable circumstances to 

 continue to preserve its species through the instru- 

 mentality of individuals of lesser development. But 

 the idea that these small specimens indicate a retrograde 

 movement towards a primitive form is, I think, contrary 

 to the general principles of Nature's workings ; because, 



