4 THE hen's egg. [chap. 



tear off laminas in a spiral direction from left to riglit, 

 from the broad to the narrow end of the egg. 



Two twisted cords called the chalazcv (Fig. 1, ch. I), 

 composed of coiled membranous layers of denser albu- 

 men, run from the two extremities of the egg to the 

 opposite portions of the yolk. Their inner extremities 

 expand and merge into a layer of denser albumen sur- 

 rounding the fluid layer next the yolk. Their outer 

 extremities are free, and do not quite reach the outer 

 layer of the white. Thus they cannot serve to suspend 

 the yolk, although they may help to keep it in position, 

 by acting as elastic pads. The interior of each chalaza 

 presents the appearance of a succession of opaque white 

 knots ; hence the name chalazae (hailstones). 



The yolk is enclosed in the vitelline membrane (Fig. 

 1, V. t), a transparent somewhat elastic membrane easily 

 thrown into creases and wrinkles. It might almost be 

 called structureless, but under a high power a fine 

 fibrillation is visible, and a transverse section has a 

 dotted or punctuated appearance ; it is probably there- 

 fore composed of fibrils. Its affinities are with elastic 

 connective tissue. 



The whole space within the viteUine membrane is 

 occupied by the yolk. To the naked eye this appears 

 tolerably uniform throughout, except at one particular 

 point of its surface, at which may be seen, lying imme- 

 diately under the vitelline membrane, a small white 

 disc, about 4 mm. in diameter. This is the blastoderm, 

 or cicatricula. 



A tolerably typical cicatricula in a fecundated egg 

 will shew an outer white rim of some little breadth, and 

 within that a circular transparent area, in the centre of 



