. Text-book of embryology. Embryology. 360 INVEETEBEATA CHAP. As development proceeds the upper portion of the egg, covered by the blastoderm, begins to be separated by a constriction from the lower part, which consists merely of yolk covered by the yolk- membrane, and so we are enabled to distinguish between "embryo" ;ind yolk-sac. It must be remem- l)ered, however, that a considerable portion of the yolk is contained within the confines of the embryo; this is known as the internal yolk- sac, and is disconnected from the external yolk-sac, which appears as an appendage. The two are,
. Text-book of embryology. Embryology. 360 INVEETEBEATA CHAP. As development proceeds the upper portion of the egg, covered by the blastoderm, begins to be separated by a constriction from the lower part, which consists merely of yolk covered by the yolk- membrane, and so we are enabled to distinguish between "embryo" ;ind yolk-sac. It must be remem- l)ered, however, that a considerable portion of the yolk is contained within the confines of the embryo; this is known as the internal yolk- sac, and is disconnected from the external yolk-sac, which appears as an appendage. The two are, of course, joined by a neck of com- Fio. 591.—Embryo of Loligo vulgaris seeu from the side and behind in order to illustrate the development of the ganglia. The embryo is younger than that repre- sented in Fig. 289. (After Faussek.) A, Embryo seen from behind. B, Embryo seen from the side, , anterior fimnel folds ; ar, rudiments of arms ; hr, rudiment of gill; eg, rudiment of cerebral ganglion ; oo, eye-cup; , eye-stalk; o(, otocyst; , posterior funnel folds ; , rudiment of pedal ganglion ; , shell- sac ; , visceral Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original MacBride, E. W. (Ernest William), 1866-1940; Kerr, John Graham, 1869-; Heape, Walter, 1855-1929. London : Macmillan
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