WHALES AND SIRENIA 91 



The Dugong, however, and the Rhytina are so far 

 whale-like in that they possess a forked tail, set, of 

 course, as in whales, and not as in fish. In the 

 Manatee the tail has another form, which, as has 

 already been mentioned, is not unsuggestive of the 

 tail of the foetus of certain whales. It is interesting 

 to notice that here, as in some other points, the 

 Dugong and the Rhytina are more whale-like, or 

 at least more purely aquatic in their structural 

 features, than is the Manatee. 



There is one small point of possible comparison 

 between the whales and the Sirenia which seems 

 to have been overlooked. It is well known that the 

 upper lip of the Manatee is cleft vertically, and that 

 the two halves of the upper lip thus divided act as 

 a pair of grasping organs for the leaves on which 

 the animal feeds. Rudiments of the same structure, 

 which are much more pronounced in the foetus, also 

 exist in the Dugong. 



Now it has often been noticed that in whales 

 between the two blow holes is a furrow. It seems 

 to be just within the bounds of possibility that this 

 groove is a still further reduction of the same 

 splitting of the lip which is so useful to the Manatee. 

 Apart from this, however, we may notice that in 

 the Sirenia the nostrils are superior in position, and 

 that in Halicore they are more so than in Manatus. 

 Another reason is to be seen here for regarding the 

 Dugong as the more perfectly modified animal of the 

 two. The external ear of the Sirenia has vanished, 

 leaving only a minute ear-hole, as in the Cetacea. 



