202 On Aquatic Carnivorous Coleoptera or Dytiscidoe. 



certain species it is so excessively slight as to be almost iuappreciable, and the 

 amount of variation to be detected in such cases being likewise very slight, one 

 cannot believe in these slight differences of development exercising any appreciable 

 effect on the existence of the creature. The sculpture however is most certainly cor- 

 relative with sex even in its rudimentary forms; thus in Dytiscus agilis (No. 825) the 

 female has the punctuation on the basal portion of the wing-cases more elongate 

 than in the male ; and in the allied Copelatus atriceps the difference is exhibited 

 in a still more rudimentary form : while in the very interesting C. dimorphus 

 (No. 827) we have a species displaying true striation in a rudimentary form, and 

 in the male in a much more rudimentary manner than in the female. And 

 throughout the fjenus, wherever there is a difference it is that the females have 

 the sculpture more developed than the males. We are entitled to believe then 

 that whatever the influences may be that have brought about in Copelatus this 

 peculiar sculpture, they are influences which have acted at first more strongly on 

 the female than on the male, but that continued during a long period such 

 disparity has disappeared, or tends to disappear. 



It may be thought that these strice were of assistance in giving holding to 

 the claws of the male, and that their direction enabled the male tarsi to arrive at 

 the position most convenient for supporting the insect during the process of 

 fertilization, and that the sculpture first gained by the female, was transmitted by 

 heredity to the other sex. But these suppositions do not seem to me very 

 satisfactory. One does not see why the females should be in the scratched species 

 more different from the males, than they are in the striate ones ; for certainly the 

 influence of heredity or sexual transference must be acting constantly, and not 

 confined to the higher forms of development of the sculpture ; and it is excessively 

 doubtful whether the highly developed sculpture is as useful for this sexual 

 function as the rudimentary form : for the beautifully perfect straight stria; and 

 grooves do not seem to me adapted at all for serving a useful purpose of the kind 

 above suggested; the twenty-four deep broad parallel striae on the wing-cases of 

 Col. sulcipennis can scarcely serve as agents to direct the claws to their requisite 

 position, and I am at a loss to see in what other way they would be useful. 

 Besides this, it is worthy of remark that in numerous species where the striation 

 has attained a great development (similar in each sex) there exists in addition a 

 very fine true sexual sculpture, peculiar to the female. The generalization of the 

 facts in accordance with any theory of common origin, or of natural selection 

 does not seem therefore to be warranted ; but on the other hand the presumption 

 that each highly developed sjDecies has reached its develojjment by passing 

 through a series of lower stages similar to such as are found still existing as the 

 maximum of development in other species, is perfectly satisfactory and indeed 

 iserristible to the imagination ; and the conclusion I come to on this subject of 

 striation is that if we could gradually subtract from a higlily developed species its 



