XII THE STOMACH 347 
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 Kiikenthal 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 Jnia, 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 com- 
plicated 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, 
v.e. close to the entry of the oesophagus, arises the second chamber, 
long and narrowish; then follows an extremely short third sac, 
1 For details and literature see Jungklaus, Jen. Zeifschr. xxxii. 1898, p. 1. | 
