GENERATION OF ANIMALS. 257 



it is becaufe they ceafe to eat ; and for this pur- 

 pofe they leave not their nefts but once a day, 

 and even then for a very Ihort time, left their 

 eggs fhould be injured by the cold. During this 

 operation, they take not above one tenth part of 

 their ordinary nourilhment. 



Animals which produce but one at a birth, ac- 

 quire nearly their full growth before they are fit 

 for generating. But thofe which produce manyj 

 generate before they are half grown. Man, the 

 horfe, the afs, the fheepj are incapable of gene- 

 ration till after they have nearly acquired their 

 full growth. It is the fame with pigeons and 

 other birds which lay only a fmall number of 

 eggs : But thofe which are more prolific, as 

 cocks and hens, fifhes, 8cc. begin to generate 

 much fooner. A cock is capable of this ope- 

 ration at the age of three months, when he is 

 not above one third of his full fize. A filh, 

 which, in 20 years, will weigh 30 pounds, ge- 

 nerates the firll or fecond year, when it weigiis 

 not, perhaps, more than half a pound. But ex- 

 periments are (till Wanting to afcertain the growth 

 and duration of fifhes : Their age maybe"dif- 

 covered by examining with a microfcope the an- 

 nual rings or llrata of which their fcales are 

 compofed. But we are ignorant how far this 

 may extend. 1 have feen, in the Qnunt de 

 Maurcpas' ponds, carps 'i\'hich were well attefted 

 to be at leaft 150 years old, and they appeared 

 to be equallv adivc and lively as common carps. 



Vol, II. ' R . I 



