{108} was till lately considered to be allied to the squirrels, and was often classed with them in the rodent order, principally on account of its dentition; at the same time that its affinities to the lemurs and apes were admitted.

The thorough investigation into its anatomy that has now been made, demonstrates that it has no more essential affinity to rodents than any other lemurine creature has.
[Illustration: THE AYE-AYE.] Bats were, by the earliest observers, naturally supposed to have a close relationship to birds, and cetaceans to fishes.

It is almost superfluous to observe that all now agree that these mammals make not even an approach to either one or other of the two inferior classes.
{109} In the same way it has been recently supposed that those extinct flying saurians, the pterodactyles, had an affinity with birds more marked than any other known animals.

Now, however, as has been said earlier, it is contended that not only had they no such close affinity, but that other extinct reptiles had a far closer one.
The _amphibia_ (_i.e._ frogs, toads, and efts) were long considered (and are so still by some) to be reptiles, showing an affinity to fishes.

It now appears that they form with the latter one great group--the ichthyopsida of Professor Huxley--which differs widely from reptiles; while its two component classes (fishes and amphibians) are difficult to separate from each other in a thoroughly satisfactory manner.
If we admit the hypothesis of gradual and minute modification, the succession of organisms on this planet must have been a progress from the more general to the more special, and no doubt this has been the case in the majority of instances.