Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 24 MOLLUSCA. The development* of the embryo' is introduced by an unequal segmentation. The segments arrange themselves in the form of a blastosphere, on which the archenteron often arises by imagination, while the rnesoderrn is developed from two cells which are early En a FIG. 502.—Stages in the development of the larva of Teredo (after B. Hatschek). </, median'section of an embryo with two mesoderm cells (3Ix) and two entoderm cells (E-i) •. EC, ectoderm cells. 4, Ciliat
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 24 MOLLUSCA. The development* of the embryo' is introduced by an unequal segmentation. The segments arrange themselves in the form of a blastosphere, on which the archenteron often arises by imagination, while the rnesoderrn is developed from two cells which are early En a FIG. 502.—Stages in the development of the larva of Teredo (after B. Hatschek). </, median'section of an embryo with two mesoderm cells (3Ix) and two entoderm cells (E-i) •. EC, ectoderm cells. 4, Ciliated embryo with mouth (O), stomach, intestine, and shell gland (Sdr); S, shell, —c, Later stage; Sp, apical plate ; A, anal invagination. separated. The first trace of the endoderm also may have the form of two cells (tig. 502). The embryo, which is partially ciliated and often rotates within the egg membranes, soon acquires a ciliated velum and shell gland. The nervous system, otocysts, and foot are not differentiated till * Vide especially Loven, ' Bidrag till Kiinnedomen /. Institute, etc., Tom. III. Vienna. 1881.
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