ANIMALS. 375 



discerned, are the first that are seen to exist j the 

 beating of the heart is perceived soon after ; the 

 less noble parts seem to spring from these j the 

 wings, the thighs, the feet, and, lastly, the bill. 

 Whatever, therefore, the animal has double, or 

 whatever it can live without the use of, these are 

 latest in production ; nature first sedulously ap- 

 plying to the formation of the nobler organs, 

 without which life would be of short continuance, 

 and begun in vain. 



The resemblance between the beginning ani- 

 mal in the egg, and the embryo in the womb, is 

 very striking ; and this similitude has induced 

 many to assert, that all animals are produced 

 from eggs, in the same manner. They consider 

 an egg excluded from the body by some, and 

 separated into the womb by others, to be actions 

 merely of one kind ; with this only difference, 

 that the nourishment of the one is kept within 

 the body of the parent, and increases as the em- 

 bryo happens to want the supply ; the nourish- 

 ment of the other is prepared all at once, and 

 sent out with the beginning animal, as entirely 

 sufficient for its future support. But leaving this 

 to the discussion of anatomists, let us proceed 

 rather with facts than dissertations ; and as we 

 have seen the progress of an oviparous animal, or 

 one produced from the shell, let us likewise trace 

 that of a viviparous animal, which is brought 

 forth alive. In this investigation, Graaf has, 

 with a degree of patience characteristic of his 

 nation, attended the progress and increase of va- 

 rious animals in the womb, and minutely marked 



