368 THE INFLUENCE OF LIVING SUEKOUNDINGS. 



selection, though not wholly prevented. Thus Kramer's calcula- 

 tion only holds good for those cases in which the causes that gave 

 rise to the occurrence of deviations from the parent species con- 

 tinue to act unchecked and uniformly, and alone determine the 

 final result. He denies, indeed, that such cases can occur, but, 

 as it seems to me, without reason. For, particularly among 

 tropical species, there is a not inconsiderable number of such 

 instances, one of which is exhibited in the accompanying cut (see 

 fig. 96) of the extreme forms of the male Cladognathus. Here, 

 according to my enumeration, the varieties standing about mid- 

 way between the two extremes represented occur in by far the 

 greatest numbers ; towards each extreme the number of indivi- 

 duals gradually diminishes, till at last, of the two extreme forms 

 only one of each was captured among hundreds of others. 



The Lamellicornes in general, beetles with flat leaf-like 

 antennae, exhibit a marked difference in the form of the two 

 sexes ; the males very frequently have large or small horns on 

 the head, while the females are usually devoid of them. This 

 is most conspicuous in the Goliath beetles, as they are called, of 

 which many species are very common in the tropics. Some- 

 times the horns of the males vaiy in a quite extraordinary degi'ee ; 

 as an illustration I here subjoin the extreme forms of the male 

 of Ghalcosoma atlas, a species mentioned by Darwin (see fig. 

 97) ; one form is the original typical Ghalcosoma atlas, of Eiich- 

 son, the other, smaller one, G. Phidias of Blainville. I have 

 captured many hundreds in the Philippine Islands, and from 

 among them have selected the two specimens here accurately 

 drawn from nature. They are the two most extreme forms of a 

 quite distinct series, and I can positively assert that they are 

 both of the same species. It can be seen that the larger indi- 

 vidual has four large horns, one of which belongs to the head 

 and three to the prothorax ; the smaller specimen shows only 

 a trace of the horn on the head; the middle horn on the pro- 

 thorax has disappeared entirely, while the two lateral horns are 

 not merely absolutely smaller, but much smaller in propor- 

 tion. 



Darwin has adduced similar cases, and not only of insects, as 

 Kramer seems to suppose, but of Crustacea, Spiders, Birds, and 



