6 



Professor Floiver 



[May 25, 



simple, conical, recurved, pointed teeth, alike on both sides and in 

 the upper and under jaws, admirably adapted for catching slippery, 

 living prey, such as fish, which are swallowed whole without mastica- 

 tion. In one genus (Pontoporia) there may be as many as sixty of 

 such teeth on each side of each jaw, making 240 in all. The more 

 usual number is from twenty to thirty. These teeth are never 

 changed, being " monophyodont," and they are, moreover, less firmly 

 implanted in the jaws than in land mammals, having never more than 

 one root, which is set in an alveolar socket which is generally wide 

 and loosely fitting, though perfectly sufficient for the simple purpose 

 which the teeth have to serve. 



Most singular modifications of this condition of dentition are met 

 with in difierent genera of toothed whales, chiefly the result of sup- 

 pression, sometimes of suppression of the greater number, combined 

 with excessive development of a single pair. In one large group, the 

 Ziphioids, although minute rudimentary teeth are occasionally found 

 in young individuals, and sometimes throughout life, in both jaws, in 

 the adults the upper teeth are usually entirely absent, and those of 

 the lower jaw reduced to two, which may be very large and projecting 

 like tusks from the mouth, as in Mesoplodon, or minute and entirely 

 concealed beneath the gums, as in Hyperoodon, — an animal which is 

 for all practical purposes toothless, yet in which a pair of perfectly 

 formed though buried teeth remain throughout life, wonderful examples 

 of the persistence of rudimentary and to all appearance absolutely 

 useless organs. Among the Delphmidce similar cases are met with. 

 In the genus Grampus the teeth are entirely absent in the upper, and 

 few and early deciduous in the lower jaw. But the Narwhal exceeds 

 all other Cetaceans, perhaps all other vertebrated animals, in the 

 specialisation of its dentition. Besides some irregular rudimentary 

 teeth found in the young state, the entire dentition is reduced to a 

 single pair, which lie horizontally in the upper jaw, and both of which 

 in the female remain permanently concealed within the bone, so that 

 this sex is practically toothless, while in the male the right tooth 

 usually remains similarly concealed and abortive, and the left is im- 

 mensely developed, attaining a length equal to more than half that of 

 the entire animal, projecting horizontally from the head in the form 

 of a cylindrical or slightly tapering pointed tusk, with the surface 

 marked by spiral grooves or ridges. 



The meaning and utility of some of these strange modifications it 

 is impossible, in the imperfect state of our knowledge of the habits 

 of the Cetacea, to explain, but the fact that in almost every case a 

 more full number of rudimentary teeth is present in early stages of 

 existence, which either disappear, or remain as concealed and function- 

 less organs, points to the present condition in the aberrant and 

 specialised forms as being one derived from the more generalised 

 type, in which the teeth were numerous and equal. 



The Mystacocetes, or Whalebone Whales, are distinguished by 

 entire absence of teeth, at all events after birth. But it is a remark- 



