the probabilities are against these orders being nearly related. Even in the skull of the Zeuglodon, which has been cited as presenting a great resemblance to that of a Seal, quite as many likenesses may be traced to one of the primitive Pig-like Ungulates (except in the purely adaptive character of the form of the teeth), while the elongated larynx,[126] complex stomach, simple liver, reproductive organs both male and female, and fœtal membranes of the existing Cetacea are far more like those of that group than of the Carnivora. Indeed it appears probable that the old popular idea which affixed the name of “Sea-Hog”[127] to the Porpoise contains a larger element of truth than the speculations of many accomplished zoologists of modern times. The fact that _Platanista_, which, as mentioned above, appears to retain more of the primitive characteristics of the group than any other existing form, and also the somewhat related _Inia_ from South America, are both at the present day exclusively fluviatile, may point to the freshwater origin of the whole group, in which case their otherwise rather inexplicable absence from the seas of the Cretaceous period would be accounted for. On the other hand, it should be observed that the teeth of the Zeuglodonts approximate more to a carnivorous than to an ungulate type. It is scarcely necessary to allude to the hypothesis started by some Continental writers to the effect that the Whales are the most primitive type of mammals with which we are acquainted, and that they are the descendants of the Mesozoic reptilian order Ichthyopterygia, from which their hyperphalangism is a direct inheritance. The Ichthyopterygia have been shown, on very strong evidence, to have been derived from land reptiles, and to have gradually acquired their hyperphalangism as an adaptive character suitable to their peculiar mode of life, and there can be but little doubt that a similar adaptation has taken place in the case of the Whales. _Suborder_ MYSTACOCETI, _the_ BALÆNOIDEA, _Whalebone, or True Whales_.[128] _Family_ BALÆNIDÆ.