VOL. LXXVII.] PHILOSOPHICAL TRANSACTIONS. 311 



class, are either entirely wanting, as the external ear ; or are placed internally, 

 as the testicles ; or are spread along under the skin, as the udder. The tail is 

 flattened horizontally, which is contrary to that of fish, this position of tail giving 

 the direction to the animal in the progressive motion of the body. I shall not 

 pursue this circumstance further than to apply it to those purposes in the animal 

 economy, for which this particular direction is intended. 



The 2 lateral fins, which are analpgous to the anterior extremities in the qua- 

 druped, are commonly small, varying however in size, and seem to serve as a 

 kind of oars. To ascertain the use of the fin on the back is probably not so easy, 

 as the large whalebone and spermaceti whales have it not ; one should otherwise 

 conceive it intended to preserve the animal from turning. I believe, like most 

 animals, they are of a lighter colour on their belly than on their back : in some 

 they are entirely white on the belly ; and this white colour begins by a regular 

 determined line, as in the grampus, piked whale, &c. : in others, the white on 

 the belly is gradually shaded into the dark colour of the back, as in the porpoise. 

 I have been informed, that some of them are pied upwards and downwards, or 

 have the divisions of colour in a contrary direction. 



The element in which they live renders certain parts which are of importance 

 in other animals useless in them, gives to some parts a different action, and 

 renders others of less account. The puncta lachrymalia with the appendages, as 

 the sac and duct, are in them unnecessary ; and the secretion from the lachrymal 

 gland is not water, but mucus, as it also is in the turtle ; and we may suppose 

 only in small quantity, the gland itself being small. The urinary bladder is 

 smaller than in quadrupeds ; and indeed there is not any apparent reason why 

 whales should have one at all. The tongue is flat, and but little projecting, as 

 they neither have voice, nor require much action of this part, in applying the 

 food between the teeth for the purpose of mastication, or deglutition, being 

 nearly similar to fish in this respect, as well as in their progressive motion. 



In some particulars they differ as much from each other as any 2 genera of 

 quadrupeds I am acquainted with. The larynx, the size of trachea, and the 

 number of ribs, differ exceedingly. The caecum is only found in some of them. 

 The teeth in some are wanting. The blow-holes are 2 in number in many, in 

 others only 1 . The whalebone and spermaceti are peculiar to particular genera : 

 all which constitute great variations. In other respects we find a uniformity, 

 which would appear to be independent of their living and moving only in the 

 water, as in the stomach, liver, parts of generation of both sexes, and in the 

 kidneys; in these last however I believe it depends in some degree on their situa- 

 tion, though it is extended to other animals, the cause of which I do not under- 

 stand. 



