elaboration of new species, by the "aimless action of Natural Selection," necessitates the granting of thirty times the number of millions of years physical considerations render it possible to allow, as Dr. Tait states the question, the difficulty of the position will not be lessened by Herr Haëckel's bold assertion, that "we have not a single rational ground for conceiving the time requisite to be limited in any way."
This writer, although he deems very slow progress to have been the rule, leaves his readers to believe in the possibility of exceptions to it. Notwithstanding the small advances made during the recent period in any line of life (how the cats, the dogs, and the pigeons of the days of the earliest Pharoahs remain represented but by pure cats and dogs and pigeons still, not one attempt at passing beyond the limit of its class having been made by any of these creatures, whose development has received such attention and studied assistance from man), they are not to be daunted by the proposition that in new centres of creation, such as New Zealand, the derivative process was by some means marvellously hastened in its accomplishment.
Recurring periods of heat and cold extending simultaneously over the greater part of the world, may be convenient agents to call into requisition for the purpose of explaining the disappearance of many forms of organic life. The vanishing of others for a time, and their return to the same localities, displacing very different ones that in the interim had flourished there, is, no doubt, due to such cause. But had these cycles been repeated more frequently than even according to the views of Mr. Croll they have been—views much more within our grasp than the consideration of processes requiring œons paralyzing to the minds of most men who attempt to dwell upon them—they would not account for many of the events which we know have taken place in the history of animal life.
Ten thousand or twenty thousand years may be deemed by evolutionists generally, periods altogether too short for the accomplishment of any of the processes of divergence and development necessary to the establishment of species, for which millions have been asked; but much could be done during such a vast lapse of years in the way of perfecting various families and the extinction of others. The recurring periods of the reign of frost over particular areas in alternate hemispheres, which have evidently taken place, would cause no violent changes, advancing as they must have done with slow enough steps to afford ample opportunity for the migration of existing forms of life to suitable situations, so long as any such remained for them to migrate to, which during this Glacial Epoch of Professor Haëckel were certainly reduced to a minimum.
There was no ice-sheet enveloping their ancient haunts, which destroyed
