INCOMPLETENESS OF THE EXPLANATION. 179 



Natural Selection leads, on the whole, to a progressive differentiation 

 of organs (division of labour), since it preserves any peculiarities 

 which are of use in the struggle for existence, and thus tends to the 

 perfection of the organism. We can therefore connect the progress 

 of simple types to higher ones with the principle of utility implied 

 by Natural Selection, without being obliged, with Niigeli, to have 

 recourse to the obscure notion of an inexplicable tendency towards 

 perfection. It is the latter mystical supposition, and not Natural 

 Selection, which is contradicted by the fact that we find a number of 

 Rhizopods, Molluscs, and Crustacea (e.g., the genera Lingula, 

 Nautilus, Limulas) have existed almost without alteration from the 

 earliest formations through all the geological periods to the present 

 time, and by the observation of a retrogression of organization in 

 the course of development (e.g., retrogressive metamorphosis of 

 Parasites). 



Nor again can it be objected that on the hypothesis of Natural 

 Selection the lower types should have been long ago suppressed 

 and have become extinct, while, as a matter of fact, there are higher 

 and lower genera in every class, and the lowest organisms are 

 nun-erous and widely distributed. It is precisely the great variety 

 in the degrees of organization which brings about and is favourable 

 to the greatest development of life, all the forms of which, both the 

 higher and the lower, being best suited to their peculiar circumstances 

 are able, more or less perfectly, to occupy a special place in nature, 

 and in a certain sense to maintain it. Even the most simple 

 organisms occupy a place in the economy of nature which can be 

 filled by no other organisms, and are necessary to the existence of 

 numerous higher grades. 



However well grounded we admit the theory of Selection to be, we 

 cannot accept it as in itself sufficient to explain the complicated and 

 involved metamorphoses which have taken place in organisms in 

 the course of immeasurable time. If the theory of repeated acts 

 of creation be rejected and the process of natural development be 

 established in its place, there is still the first appearances of organisms 

 to be accounted for, and especially the definite course which the 

 evolution of the complicated and more highly developed organisms 

 has ta'ken has to be explained. In the many wonderful phenomena 

 of the organic world, amongst others in the origin of Man in the 

 diluvial or tertiary period, we have a riddle the solution of which 

 must remain for future investigators. 



