ON GENERATION. 415 



the seed and fruit of plants ; in the same way as it is to the 

 egg of oviparous creatures ; to worms in spontaneously engen- 

 dered animals, or to certain vesicles fruitful by the vital warmth 

 of their included moisture. In each and all of these the same 

 things inhere which might with propriety lead to their being 

 called seeds; they are all bodies, to wit, from which and by 

 which, as previously existing matter, artificer and organ, the 

 Avhole of au animal body is primarily engendered and pro- 

 duced. 



The other structure is the embryo produced from the seed 

 or conception. For both the matter and the moving and effi- 

 cient cause, and the instruments needful to the operation, must 

 necessarily precede operation of any and every kind. 



We have already examined the structure of the egg. Now 

 the embryo to which it gives birth, in so far as this can be 

 made out by observation and dissection, particularly among the 

 more perfect animals with [red] blood, appears to be perfected by 

 four principal degrees or processes, which we reduce to as many 

 orders, in harmony with the various epochs in generation ; and 

 we shall demonstrate that what transpires in the egg also takes 

 place in every conception or seed. 



The first process is that of the primogenial and genital part, 

 viz. the blood with its receptacles, in other words, the heart 

 and its vessels. 



And this part is first engendered for two principal reasons : 

 1st, because it is the principal part which uses all the rest as 

 instruments, and for whose sake the other parts are formed; 

 and, 2d, because it is the prime genital part, the origin and 

 author of the rest. The part, in a word, in which inhere both 

 the principle whence motion is derived, and the end of that mo- 

 tion, is obviously father and sovereign. 



In the generation of this first part, which in the egg is ac- 

 complished in the course of the fourth day, although I have not 

 been able to observe any order or sequence, inasmuch as the 

 whole of its elements, the blood, the vessels, and the pulsating 

 vesicles appear simultaneously, I have nevertheless imagined, 

 as I have said, that the blood exists before the pulse, because, ac- 

 cording to nature's laws, it must be antecedent to its receptacles. 

 For the substance and structure of the heart, namely, the conical 

 mass with its auricles and ventricles, as they are produced long 



