116 NATURAL HISTORY. 



two different causes. The first is, for that creatures 

 which have a definite and exact shape (as those have 

 which are procreated by copulation,) cannot be pro 

 duced by a weak and casual heat ; nor out of matter 

 which is not exactly prepared according to the species. 

 The second is, for that there is a greater time required 

 for maturation of perfect creatures : for if the time re 

 quired in vivification be of any length, then the spirit 

 will exhale before the creature be mature ; except it be 

 enclosed in a place where it may have continuance of 

 the heat, access of some nourishment to maintain it, 

 and closeness that may keep it from exhaling : and 

 such places are the wombs and matrices of the.fe- 

 males. 1 And therefore all creatures made of putrefac 

 tion are of more uncertain shape ; and are made in 

 shorter time ; and need not so perfect an inclosure, 

 though some closeness be commonly required. As for 

 the Heathen opinion, which was, that upon great mu 

 tations of the world, perfect creatures were first engen 

 dered of concretion ; as well as frogs, and worms, and 

 flies, and such like, are now ; 2 we know it to be vain : 

 but if any such thing should be admitted, discoursing 

 according to sense, it cannot be, except you admit a 

 chaos first, and commixture of heaven and earth. For 

 the frame of the world, once in order, cannot effect it 

 by any excess or casualty. 



1 Compare Telesius, De Rerum Natura, vi. 

 a Plut. De Placitis Philos. v. 19. 



