THE AMPHIBIOUS CARNIVORA. 69 



It is also deserving of remark, that they are decid- 

 edly migratory in their habits, the great stimulus to 

 which appears to be the change of temperature. Very 

 many are, from choice, inhabitants of the margins of 

 the frozen seas towards both poles. But the line of 

 the margin varies much with the season of the 

 year. On the approach of the Polar winter they 

 emerge from its dark and dreary solitude towards 

 milder regions, and during the winter months select 

 a more moderate temperature, where they are 

 occupied with the all-important, work of parturition. 

 Their period of gestation is considered to be nine 

 or ten months, and their progeny never exceeds 

 one, or at most two, at a time. In the herbivorous 

 Cete the mammae are pectoral, whilst in the amphi- 

 bia they are ventral. Their number, in some 

 species of Seals, is said to be two, and in others 

 four; the teats lie concealed in the skin, so defending 

 them from the exposure arising from their crawling 

 when on land. Thus placed, the nipples are 

 seized by the young with more difficulty than is 

 usual ; and to assist them, it has been alleged that 

 the tongue has received that bifurcated termination, 

 which is seen in the margin, which is a curious 

 feature in many, if not all Seals, and is, we be- 

 lieve, more conspicuous in them than in any other 

 of the Mammalia. 



