Royal Society, 229 



accordingly proposed tlie following as the formula of the normal or 

 functional dentition of the Walrus : — 



.1-1 1 — 1 3—3 1 o 



But, as might be expected in a dentition deviating so remarkably from 

 that of other Mammals of the same order, varieties are not unfre- 

 quently met with in the number of the teeth of the Walrus. Pro- 

 fessor Owen cited instances of such varieties in ten skulls of the 

 Walrus, of different ages and sex. The result of which was, that 

 occasionally a small tooth was found anterior to the normal series of 

 four, and more commonly in the upper than in the lower jaw ; and 

 that, more rarely, a small tooth was superadded behind the normal 

 four, in the upper jaw, and still more rarely in the lower jaw : the 

 formula of the dentition of such varieties, in excess, being, — 



■ 2—2 1 — 1 3—3 1 — 1 or 



^^2' ''o=ro> P5=5' ^« 1=1=26. 



The additional anterior small incisor was due cither to the reten- 

 tion and growth of the first deciduous denticle, or to the develop- 

 ment of a small successor to it. The additional posterior grinder was 

 due to the occasional development of a germ in the back part of the 

 gum or jaw. The minute milk-teeth relate, by their gubernacula, to 

 the development of the permanent teeth, but seem never to be put to 

 use themselves; the milk- canine was buried in the gum outside the 

 protruded point of the permanent canine ; so that this tooth is extri- 

 cated and cuts the guni before the tooth of which it is the successor 

 makes its appearance, that tooth being probably removed by absorp- 

 tion. Here, therefore, was another instance, analogous to that of the 

 rudimental teeth in the foetal Whale, of parts developed without any 

 obnous office as organs of mastication, but serving to illustrate the 

 relation of adhesion to a more normal type of dentition. In conchi- 

 sion. Professor Owen remarked that the food of the Walrus consisted, 

 in a state of nature, of sea-weed, crustaceans and mollusks ; and that 

 although, by the totality of its organization, it must be placed near 

 the Seals, and with them be classed in the order Carnivora, yet that 

 the incisors and premolars were alike well adapted to pound marine 

 plants, and to break and crush shells. Fragments of a bivalve shell, 

 a species o^ Mya, had been found with pounded sea-weed, by the 

 Surgeon of Parry's Polar Expedition, in the stomach of a full-grown 

 Walrus. The great descending canine tusks serve as weapons of 

 offence and defence, and to aid the animal in mounting and clamber- 

 ing over ice-blocks, bergs and floes in the Arctic Seas, in which the 

 Walrus has been organized to enjoy its existence. 



KOYAL SOCIETY. 



November 23, 1854.— Thomas Bell, Esq., V.P., in the Chair. 



" On the Impregnation of the Ovum in the Stickleback." By 

 W. H. Ransom, M.D. 



I purpose placing before the Royal Society in this communication, 



