by what you call evolution. The reproductive faculty of the males and the females of this distinct and peculiar animal is limited to the generative reproduction of individuals of the same type, by a sexual union of two individuals of that type. Their progeny, in successive generations, may be marked by adventitious and slowly acquired peculiarities; but unless there can be found some instance or instances in which the process of modification has resulted in an animal which we must regard as an 'essentially new creature--a new species--what becomes of the auxiliary evidence which is supposed to be derived from the effects of interbreeding between those individuals which can interbreed? I lose all hold upon the theory of evolution, unless I can have some proof that natural and sexual selection have overcome the barriers against a sexual union among animals which are divided into males and females of the several species, each of which is placed under a law of procreation and gestation peculiar to itself, and never produces any type but its own. KOSMICOS. You wander from the principle of evolution. I have to be perpetually restating it. Observe, then, that there are multitudes of facts which warrant the belief that, starting with any one kind of animal organism, however peculiar and distinct, the struggle for existence among the enormous number of individuals of that animal becomes most intense, and a furious battle is constantly going on. The best-appointed males, in the fierceness of the strife for possession of the females, develop new organs and powers, or their original organs and powers are greatly enhanced. Their descendants share in these modifications; and the modifications go on in a geometrical ratio of increase through millions of years, until at some time there is developed an animal which differs absolutely from its remote progenitors which were away back in the remote past, and which began the struggle for individual life and the continuation of their species or their race in a condition of things which left the fittest survivors the sole or nearly the sole propagators of new individuals. This struggle for existence may have begun--probably it did begin--before the separation of the sexes, when the organism was unisexual or even asexual. That is to say, there may have been, and there probably was, an organism which multiplied with enormous rapidity, without the bisexual method of reproduction. The vast multitude of such individuals would lead to the destruction of the weakest; the strong survivors would continue to give rise to other individuals, modified from the original type, until at length, by force of this perpetual exertion and struggle and the survival of the fittest, modifications of the method of reproduction would ensue, and the bisexual division would be developed and perpetuated.