STEUCTUKE OF THE EGG. 



291 



men, salivary matter, and the common sulphates and hydro- 

 chlorates in" small quantity. The chalazce (figs. 287, ff, ff, 

 320, b, b) are a couple of spirally-twisted ropes, composed of 

 delicate fibres, or of a fine membrane, which, as the chalazi- 

 ferous membrane (membrana chalazifera), closely surrounds 

 the yolk, and then going off in the fashion of a funnel towards 

 either pole of the egg, becomes twisted into a rope (figs. 287 

 and 318, 320). A white streak, in the shape of a band, may 

 usually be seen extending over the 

 yolk from one chalaza to the other ; 

 this is the zone or belt (zond), which, 

 however, is not constant, and is 

 of no particular importance. The 

 chalazae vary exceedingly in point 

 of form and development ; they 

 appear to consist of coagulated al^ 

 bumen. The yolk, or yolk-ball 

 (vitellus), is somewhat lighter than 

 the white, so that, in whatever 

 position the egg is held, it always 

 rises towards the side that is up- 

 permost. The vitellary membrane 

 (cuticula vitelli) (fig. 319, a) is 

 a perfectly simple, transparent, 

 and slightly glistening membrane. 

 It closely surrounds the yolk 

 (fig. 287, i). Immediately under 

 the vitellary membrane, and at 

 a point which in an opened egg 

 is always directed upwards, the 

 cicatricula (fig. 320, A, c, and 

 B), or tread, is seen shining 

 through in the shape of a round 

 whitish spot. The cicatricula con- 

 sists superficially of a membra- 

 nous stratum (stratum proligerum 

 fig. 320, B), from a line and a 

 half to two lines in diameter, in which the germinal vesicle 

 was imbedded at an earlier period. This is the germ from 

 which in the beginning of the brooding the germinal mem- 

 brane, blastoderma, is produced. The germ in recent eggs 



u 2 



Fig. 319. Vitellus, or yolk 

 of a hen's egg, seen from 

 above; a, a, vitelline mem- 

 brane ; b, vitellus ; c, c, ha- 

 lones ; d, darker, more exter- 

 nal part of the germ (the fu- 

 ture area vasculosa) ; e, cen- 

 tral transparent part of the 

 germ (the future area pelluci- 

 da). In the yolk here figured, 

 the first slight effects of incu- 

 bation are apparent viz., in 

 the separation in the germ, 

 which often takes place from 

 transient exposure of the egg 

 to a high temperature (hand- 



temperature of the air 

 been high. 



has 



