174 A HISTORY OF 



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 embryo hap- 

 pens to want the supply ; the nourishment 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 the changes they un- 

 dergo. Having dissected a rabbit, half an hour after impregnation, 

 he perceived the horns of the womb, that go to embrace and com- 

 municate with the ovary, to be more red than before ; but no other 

 change in the rest of the parts. Having dissected another, six hours 

 after, he perceived the follicules, or the membrane covering the eggs 

 contained in the ovary, to become reddish. In a rabbit dissected 

 after twenty-four hours, he perceived, in one of the ovaries, three 

 follicules, and, in the other, five, that were changed ; being become, 

 from transparent, dark and reddish. In one dissected after three 

 days, he perceived the horns of the womb very strictly to embrace 

 the ovaries ; and he observed three of the follicules in one of them, 

 much longer and harder than before ; pursuing his inquisition, he also 

 found two of the eggs actually separated into the horns of the womb, 

 and each about the size of a grain of mustard-seed ; these little eggs 

 were each of them inclosed in a double membrane, the inner parts 

 being filled with a very limpid liquor. After four days, he found, in 

 one of the ovaries, four, and, in the other, five follicules, emptied 

 of their eggs ; and in the horns correspondent to these, he found an 

 equal number of eggs thus separated ; these eggs were now grown 

 larger than before, and somewhat of the size of sparrow-shot. In 

 five days, the eggs were grown to the size of duck-shot, and could 

 be blown from the part of the womb where they were, by the breath. 

 lit seven days, these eggs were found of the size of a pistol-bullet, 

 each covered with its double membrane, and these much more dis- 

 linct than before. In nine days, having examined the liquor contained 

 in one of these eggs, he found it, from a limpid colour, less fluid, to 

 have got a light cloud floating upon it. In ten days, this cloud began 

 to thicken, and to form an oblong body, of the figure of a little 

 worm : and, in twelve days, the figure of the embryo was distinctly to 

 be perceived, and even its parts came into view. In the region of 

 the bieast he perceived two bloody specks ; and two more that ap- 

 peared whitish. Fourteen days after .impregnation, the head of the 

 embryo was become large and transparent, the eyes prominent, the 

 mouth open, and the rudiments of the ears beginning to appear ; the 

 back-bone, of a whitish colour, was bent towards the breast ; the 

 two bloody specks being now considerably increased, appeared ti oe 

 nothing less tnan the outlines of the two ventricles of thr. heart; lad 



