Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . nt which in an opened egg the first dight effects of incu- ,. , r , bation are apparent— in is always directed upwards, the the separation in the germ, cicatricula (fig. 320, A, c, and which often takes place fromB), or tread, is seen shining transient exposure of the eggthrough in the shape of a round to a hiSh temperature (hand-whitish spot. The cicatricula con- ^g) or when the eggs haver- • n i- been laid some time, and the sists
Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . nt which in an opened egg the first dight effects of incu- ,. , r , bation are apparent— in is always directed upwards, the the separation in the germ, cicatricula (fig. 320, A, c, and which often takes place fromB), or tread, is seen shining transient exposure of the eggthrough in the shape of a round to a hiSh temperature (hand-whitish spot. The cicatricula con- ^g) or when the eggs haver- • n i- been laid some time, and the sists superficially of a membra- temperature of the air hasnous stratum (stratum proligerum been high.—fig. 320, B), from a line and a half to two lines in diameter, in which the germinal vesiclewas imbedded at an earlier period. This is the germ fromwhich in the beginning of the brooding the germinal mem-brane, blastodernia, is produced. The germ in recent eggs u 2 Fig. 319.—Vitellus, or yolkof a hens egg, seen fromabove; a, a, vitelline mem-brane ; b, vitellus; c, c, ha-lones ; d, darker, more exter-part of the germ (the fu- ceu- 292 EMBRYOLOGY. I. is generally slightly adherent to the vitellary membrane; in such as havebeen kept forsome time, itis more de-tached ; un-der all circum-stances it isreadily difflu-ent, little con-sistent. Inthe centre itis somewhatclearer andmore transpa-rent than else-where (, e), andallows thegerminal cu-«,«/„, (ciirmi- I If, LI/ 1 ttO • I O It //C-Cv 7 , > , lusprohgerm) to be seen through it. This germinal cumulus is a loose whitish-yellow,and somewhat conically formed granular layer, sunk in thesubstance of the yolk ; betwixt it and the discus proliyerus,or germinal disc, there is a minute interval, which is filledwith a fluid that appears to communicate with the canal ofthe central cavity of the yolk.*
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1870
