172 A HISTORY OF 



midst of which the embryo was seen to reside. The embryo re 

 sembled a composition of little threads, which the warmth of future 

 incubation tended to enlarge, by varying and liquifying the other 

 fluids contained within the shell, and thus pressing them either into 

 the pores or tubes of their substance. 



Upon placing the eggs in a proper warmth,* either under the sun, 

 or in a stove, after six hours the vital speck begins to dilate, like the 

 pupil of the eye. The head of the chicken is instantly seen, with 

 the back bone, something resembling a tadpole, floating in its ambient 

 fluid, but as yet seeming to assume none of the functions of animal 

 life. In about six hours more the little animal is seen more distinctly ; 

 the head becomes more plainly visible, and the vertebrae of the back 

 more easily perceivable. All these signs of preparation for life are 

 increased in six hours more : and at the end of twenty-four, the ribs 

 begin to take their places, the neck begins to lengthen, and the head 

 to turn to one side. 



At this time, f also, the fluids in the egg seem to have changed 

 place ; the yolk, which was before in the centre of the shell, ap- 

 proaches nearer to the broad end. The watery part of the white is, 

 in some measure, evaporated through the shell, and the grosser part 

 sinks to the small end. The little animal appears to turn towards the 

 part of the broad end, in which a cavity has been described, and with 

 its yolk seems to adhere to the membrane there. At the end of 

 forty hours the great work of life seems fairly begun, and the animal 

 plainly appears to move ; the back bone, which is of a whitish colour, 

 thickens ; the head is turned still more on one side ; the first rudiments 

 of the eyes begin to appear, the heart beats, and the blood begins 

 already to circulate. The parts, however, as yet are fluid ; but, by 

 degrees, become more and more tenacious, and hardened into a kind 

 of jelly. At the end of two days, the liquor in which the chicken 

 swims, seems to increase ; the head appears with two little bladders 

 in the place of eyes ; the heart beats in the manner of every embryo 

 where the blood does not circulate through the lungs. In about four- 

 teen hours after this, the chicken is grown more strong ; its head, 

 however, is still bent downwards ; the veins and arteries begin to 

 branch, in order to form the brain ; and the spinal marrow is seen 

 stretching along the back bone. In three days the whole body of the 

 chicken appears bent ; the head, with its two eye-balls, with their 

 different humours, now distinctly appear ; and five other vessels are 

 seen, which soon unite to form the rudiments of the brain. The 

 outlines also of the thighs and wings begin to be seen, and the body 

 begins to gather flesh. At the end of the fourth day, the vesicles, 

 that go to form the brain, approach each other ; the wings and thighs 

 appear more solid ; the whole body is covered with a jelly-like flesh ; 

 the heart, that was hitherto exposed, is now covered up within the 

 body, by a very thin transparent membrane ; and, at the same time, 

 the umbilical vessels, that unite the animal to the yolk, now appear to 

 come forth from the abdomen. After the fifth and sixth days, the 

 vessels of the brain begin to be covered over ; the wings -Mid thigh* 



MalpighL f Harvey. 



