THE STOMACH 347 



them — are literally double teeth. This is a suggestion of the 

 more complicated teeth of the Zeugiodoiits, and shows so far 

 that tlie 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, Init 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 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 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 Euminants — 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 Eorqual has a stomach with as few compaitments as any. 

 The only Whale which appears to have fewer is Balaena mysticetus, 

 where there are but three. In the Eorqual 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, 



^ For details and literature see Jiuigklaus, Jen. Zeitschr. xxxii. 1898, p. 1. 



