128 THE CANADIAN NATURALIST. [June 



from auy definite conclusions as to the general law of succession 

 and its relations to physical changes. 



The application of these questions to the animals referred to by 

 Owen, will serve farther to shew their significance as to limi- 

 tations of derivation. Pictet catalogues eleven species of Eocene 

 Paloeotheria. Without inquiry as to the origin of these, let us 

 confine ourselves to their progress. Under tl e hypothesis of 

 derivation, each of these had capacities for improvement, probably 

 all leading to that line of change ending in the production of the 

 horse. If so, then each of our Palaeotheria, passing through 

 intermediate changes, may be the predecessor of some of the 

 equine animals of the Post-pliocene and Modern periods. But if, 

 as seems probable, the time intervening between the Eocene 

 and the Modern was unfavourable to the multiplication of 

 such species, then several may have perished utterly in the 

 process, and all might have perished. Supposing, on the 

 contrary, the time to have been favourable to the increase of such 

 creatures, we might have had hundreds of species of equine 

 animals instead of the small number extant at present. Again, 

 what possibilities of change remain in the horse ? Can he be 

 supposed capable of going on still f\irther in the direction of his 

 progress from Palseotherium, or has he attained a point at which 

 further change is impossible ? Will he then, in process of time, 

 wheel round in his orbit and return to the point from which he 

 set out ? Or will he continue unchanged until he becomes 

 extinct? Or can he at a certain point diverge into a new series 

 of changes ? We do not know any Palaeotherium betore the 

 Eocene. Is it not possible that they may have originated in some 

 way different from that slow change by which they are supposed 

 to have been transmuted into horses, and that in their first origin 

 they were more plastic than after many changes had happened 

 to them ? May it not be that the origin of forms or types is 

 after all something different from derivative changes, and that 

 new forms are at first plastic, afterwards comparatively fixed — at 

 first fertile in derivative species, and afterward comparatively 

 barren. Certainly, unless something of this kind is the case, we 

 fail to find in the Modern world a sufficient number of re- 

 presentatives of the Palaeotheria, Anoplotheria, Lophiodons, 

 Elephants and Mastodons of the tertiary. On the other hand, it 

 is scarcely possible to find a sufficient starting point in the 



