64 



OVUM. 



colour seems to be merely a uniform tinge of 

 the outermost layer of calcareous matter.* 



The lining membrane of the shell is a 

 peculiar fibrous, interwoven structure, depo- 

 sited in laminae of some thickness and tough- 

 ness, which is readily divided by tearing into 

 two layers over the whole surface of the 

 egg an outer, thicker, and denser, adhering 

 firmly to the inner surface of the shell j and an 

 inner, thinner, smoother, and of finer texture, 

 which may be easily withdrawn from the 

 outer one, and which naturally separates from 

 it at the air-space ; but both the outer and 

 inner layers of this membrane may be torn 

 into a number of thinner laminae, all agreeing 

 in their minute structure. 



By microscopic examination, this membrane 

 is found to consist of a closely-interwoven 

 network of peculiar fibres, which are of va- 

 rious sizes, generally between 8b * 00 th and 

 ^._u_th of an inch in diameter ; the larger fre- 

 quently branching into or giving off smaller 

 fibres at acute angles, the sides rendered un- 

 even by minute projections or knots upon 

 them (not represented in the figure) ; the 

 larger fibres are of a somewhat flattened or 

 ribband-like form. The external layer of the 

 membrane contains the largest fibres. These 

 fibres appear to be analogous in their che- 

 mical nature to those of the elastic yellow 

 texture, not being soluble in strong acetic 

 acid ; but they do not coil up in the manner 

 of the elastic tissue (see fig. 45. A). 



The parchment-like coverings of the eggs 

 of serpents and lizards, which have no calca- 

 reous shell, seem to be composed of a greater 

 number of layers of the fibro-laminar texture 

 now described. 



The albumen, or white of the egg, compre- 

 hends several layers of glairy, albuminous, 

 semifluid substance deposited round the yolk, 

 the chalazae, or grandines, or twisted cords, 

 and the condensed layer of albumen, forming 

 a thin membranous investment immediately 

 over the yolk membrane. In a perfectly-fresh 

 egg, or in an egg taken from the oviduct pre- 

 viously to its being laid, the whole albumen 

 has the consistence of a moderately-firm 

 jelly ; but very soon the outer part becomes 

 fluid, and allows of the freer motion of j the 

 parts within the shell. This solution of the 

 albumen proceeds to a greater extent after 

 some hours' incubation, especially over the 

 cicatricula. 



The deeper part of the albumen, or that 

 next the yolk, is more dense in consistence. 

 No part of it, when unchanged by reagents, 

 presents any sensible structure either to the 

 naked eye or when viewed microscopically. 

 If, however, the soft contents of a fresh egg, 

 or one removed from the oviduct, be taken 

 from within the shell, and thrown into water 

 either pure or with a little acetic acid mixed 

 with it, a slight turbidity or coagulation of 

 the albumen takes place on the surface, which 

 brings out the appearance of a spiral arrange- 



* See the works of Hewetson and others on the 

 Eggs of Birds. Carus and Otto, Erlauterungstafelu 

 der Vergleich. Anat. part v. 



ment of laminae ; and in a boiled egg these 

 laminae may be torn in great numbers in suc- 

 cession from off it, the direction pf the spiral 

 being from left to right, from the large towards 

 the small end of the egg. With a little 

 care, almost the whole of the albumen may 

 thus be wound off the egg in spiral strips, 

 the deeper ones enclosing the twisted cha- 

 lazae (see^g. 46. n). 



The coagulated albumen presents, in the 

 microscope, a minute but indefinite granular 

 structure. 



The chalazcB (grandines) are two irregularly- 

 twisted cords of albumen, harder than the rest, 



Fig. 46. 



Manner in which the chalazce, albumen, 8fc., are 

 deposited round the ovarian ovum of the Fowl. 



A. Yolk from the upper part of the oviduct soon 

 after it has entered it, showing a thin covering of 

 albumen on the yolk, forming the chalaziferous 

 membrane, and the twisted chalazae extending from 

 the opposite poles of the yolk. The twisting in 

 these is represented more strongly than it can be 

 seen at this period. 



B. Sketch of the fully formed chalazae from 

 opposite sides of the yolk, stretched to their full 

 length, and showing the opposite direction of the 

 spiral in each. 



c. Egg from above the middle of the oviduct ; 

 the first layers of albumen deposited round the yolk 

 and chalazoe. 



