ANIMALS. 



127 



the shell lies that common membrane, or 

 skin, which lines it on the inside, adhering 

 closely to it every where, except at the broad 

 end, where a little cavity is left, that is filled 

 with air, which increases as the animal with- 

 in grows larger. Under this membrane are 

 contained two whites, though seeming to us 

 to be only one, each wrapped up in a mem- 

 brane of its own, one white within the other. 

 In the midst of all is the yolk, wrapped round 

 likewise in its own membrane. At each end 

 of this are two ligaments, called chalazae, 

 which are, as it were, the poles of this micro- 

 cosm, being white dense substances, made 

 from the membranes, and serving to keep the 

 white and the yolk in their places. It was 

 the opinion of Mr. Derham, that they served 

 also for another purpose ; for a line being 

 drawn from one ligament to the other, would 

 not pass directly through the middle of the 

 yolk, but rather towards one side, and would 

 divide the yolk into two unequal parts, by 

 which means these ligaments served to keep 

 the smallest side of the yolk always upper- 

 most ; and in this part he supposed the cica- 

 tricula, or first speck of life, to reside ; which, 

 by being uppermost, and consequently next 

 the hen, would be thus in the warmest situ- 

 ation. But this is rather fanciful than true, 

 the incipient animal being found in all situa- 

 tions, and not particularly influenced by 

 any.* The cicatricula, which is the part 

 where the animal first begins to show signs 

 of life, is not unlike a vetch, or a lentil, lying 

 on one side of the yolk, and within its mem- 

 brane. All these contribute to the little ani- 

 mal's convenience or support; the outer 

 membranes and ligaments, preserve the fluids 

 in their proper places ; the white serves as 

 nourishment ; and the yolk, with its mem- 

 branes, after a time, becomes a part of the 

 animal's body. b This is the description of a 

 hen's egg, and answers to that of all others, 

 how large or how small soever. 



Previous to putting the eggs to the hen, 

 our philosophers first examined the cicatri- 

 cula, or little spot, already mentioned ; and 

 which may be considered as the most im- 

 portant part of the egg. This was found, in 

 those that were impregnated by the cock, to 



Mailer. 



b Ibid. 



be large ; but in those laid without the cock, 

 very small. It was found by the microscope, 

 to be a kind of bag, containing a transparent 

 liquor, in the midst of which the embryo was 

 seen to reside. The embryo resembled a 

 composition of little threads, which the 

 warmth of future incubation tended to en- 

 large, by varying and liquefying 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, c 

 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 distinctly seen, with the back-bone, some- 

 thing resembling a tadpole, floating in its am- 

 bient 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 prepa- 

 ration for life are increased in six hours more : 

 and, at the end of twenty-four hours, the ribs 

 begin to take their places, the neck begins 

 to lengthen, and the head to turn to one side. 



At this time, d 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 wa- 

 tery 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 harden 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 



Malpighi. 



Harvey. 



