We have dwelt at length upon this subject, because of its great general importance, and because we believe that Professor Kolliker's criticisms on this head are based upon a misapprehension of Mr. Darwin's views—substantially they appear to us to coincide with his own. The other objections which Professor Kolliker enumerates and discusses are the following*:—([Footnote] *Space will not allow us to give Professor Kolliker's arguments in detail; our readers will find a full and accurate version of them in the 'Reader' for August 13th and 20th, 1864.)
"1. No transitional forms between existing species are known; and known varieties, whether selected or spontaneous, never go so far as to establish new species."
To this Professor Kolliker appears to attach some weight. He makes the suggestion that the short-faced tumbler pigeon may be a pathological product.
"2. No transitional forms of animals are met with among the organic remains of earlier epochs."
Upon this, Professor Kolliker remarks that the absence of transitional forms in the fossil world, though not necessarily fatal to Darwin's views, weakens his case.
"3. The struggle for existence does not take place."
To this objection, urged by Pelzeln, Kolliker, very justly, attaches no weight.
"4. A tendency of organisms to give rise to useful varieties, and a natural selection, do not exist.
"The varieties which are found arise in consequence of manifold external influences, and it is not obvious why they all, or partially, should be particularly useful. Each animal suffices for its own ends, is perfect of its kind, and needs no further development. Should, however, a variety be useful and even maintain itself, there is no obvious reason why it should change any further. The whole conception of the imperfection of organisms and the necessity of their becoming perfected is plainly the weakest side of Darwin's Theory, and a pis aller (Nothbehelf) because Darwin could think of no other principle by which to explain the metamorphoses which, as I also believe, have occurred."
Here again we must venture to dissent completely from Professor Kolliker's conception of Mr. Darwin's hypothesis. It appears to us to be one of the many peculiar merits of that hypothesis that it involves no belief in a necessary and continual progress of organisms.