258 VARIETIES IN THE 



I will not fay with Leeuwenhoek, that fifhes 

 are immortal, or, at leaft, that they cannot die 

 of old age. Every thing, in time, muft perifh. 

 .Whatever has an origin, a birth, or commence- 

 ment, muft arrive at a termination or death. 

 But fifhes, by living in a uniform element, and 

 being fheltered from the injurious viciflitudes of 

 the air, muft continue longer in the fame ftate 

 than other animals, efpecially if thefe vicifTitudes, 

 as Bacon remarks, be the chief caufes of the 

 deftruQion of animated beings. But the prin- 

 cipal caufe of the longevity of filhes is, that their 

 bones are fofter than thole of other animals, and 

 do not perceptibly harden with age. The bones 

 of fifhes lengthen, and turn thick without ac- 

 quiring more folidity. But the denfity of the 

 bones of other animals continually increafes ; 

 and, when their interftlces are completely filled 

 and obftrud:ed, the circulation of their fluids 

 ceafes, and death enfues. • But, in the bones of 

 fifhes, this augmentation of folidity, which is the 

 natural caufe of death, proceeds in fuch an im- 

 perceptible manner, that they muft live very 

 long before they can feel any of the effeds of 

 old age. 



All quadrupeds covered with hair are vivipa- 

 rous, and thofe covered with fcales are ovipa- 

 rous. The clofe texture of the fhells or fcales 

 of oviparous animals prevents them from lofing 

 fo much matter by tranfpiration, as makes its 

 way through the porous fkins of the viviparous. 



May 



