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 them—are literally double teeth. This is a suggestion of the more complicated teeth of the Zeuglodonts, and shows so far that the simple conical teeth of existing Whales (cf. however the Platanistidae) are not by any manner of means so primitive as their actual structure would undoubtedly lead one to believe. Further than this, the greater number of teeth in the older embryo coincided with the disappearance of these double teeth, which seem to split up into the simple conical teeth.

The Toothed Whales are not furnished with baleen, but with teeth only. These teeth are more or less numerous, their arrangement being of value in the classification of the group; a matter which is dealt with later.

In the Narwhal, whose dentition in the adult is reduced to the well-known tusk or tusks (properly developed only in the male), there is a complete foetal dentition. A very curious fact has been elucidated by Professor Kükenthal about the dentition of the Common Porpoise. It appears that in this Cetacean the two teeth corresponding to each other of the two dentitions may fuse into a single tooth, which has in consequence a double crown. It may be that this is the case with the Platanistid Inia, and that its diconodont teeth are not, therefore, a reminiscence of the comparatively complicated teeth of the ancient Zeuglodonts.

The internal organs of Whales which show the greatest peculiarities as compared with other mammals are the stomach, the lungs, and the diaphragm. Whales always possess a complicated stomach divided into many, but into a variable number of, chambers: there are as few as four in some, as many as fourteen in Ziphioids.

On account of its complication the stomach has been compared to that of Ruminants—it has even been alleged that Whales "ruminate"—but the comparison will not hold good. Nor, on the other hand, is there a very close resemblance to the equally-complicated stomach of the Sirenians.

The Rorqual has a stomach with as few compartments as any. The only Whale which appears to have fewer is Balaena mysticetus, where there are but three. In the Rorqual the oesophagus opens into a more or less globular sac; from the upper end of this, i.e. close to the entry of the oesophagus, arises the second chamber, long and narrowish; then follows an extremely short third sac,