OF NATURAL HISTORY. 75 



own provifions. When he reaches the confines of tho 

 defert, he robs the fir ft pafTengers who come in his way, pil- 

 lages the folitary houfes, loads his camels with the booty, 

 and, if purfued, he accelerates his retreat. On thefe occa- 

 fions he difplays his own talents as well as thofe of his camels. 

 He mounts one of the iieeteft, condufls the troop, and oblio-- 

 es them to travel day and night, without almoft either flop- 

 ping, eating, or drinking ; and, in this manner, he often 

 performs a journey of SOO leagues in eiglit days. 



Another order of quadrupeds deferves our notice. Thofe 

 which have been diftinguiflied by the appellation of amphib- 

 ious, are capable of remaining a long time under water. 

 They live chiefly upon fifhes, and, without this faculty of 

 continuing a confiderable time under water, they would be 

 unable to procure their food. To this tribe belong the feal, 

 the walrus, the manati, the fea-lion, 8cc. The feal and wal- 

 rus are mors nearly allied to land-quadrupeds than to 

 the cetaceous animals ; becaufe they have four diftlncH: 

 legs, though nothing but the feet project beyond the flcin. 

 The toes of the feet are all connected by membranes, vdiicli 

 enable thefe animals to Avim in queft of their prey. They 

 differ from terreftrial quadrupeds by the fingular faculty of 

 living with equal eafe either in air or inwater. This pecu- 

 liarity of economy and manners prefuppofes the neceflity of 

 fome deviation from the general ilrudlure of quadrupeds ; 

 and Nature has accomplifhed this purpofe by a very fimple 

 artifice. 



In man, and in all land-quadrupeds, the lungs of the foetus? 

 have no motion, and receive no more blood than is requifite 

 for their growth and nourifliment. But, immediately after 

 birth, the young animals refpire, and the whole mafs of 

 blood circulates through their lungs. To carry on the cir- 

 culation in the foetus ftate, another pafTage was necefTary. 

 The blood in the right auricle of the heart, inftead of pafTm^ 



