. Text-book of embryology. Embryology. IX MOLLUSCA 311 which span the blastocoele, extending from gut to ectoderm. In A _ „ B ph- Fig. 245.—Formation of the coelom iu Paludina mvipara. (After Brlanger.) A, optical frontal section of embryo in the stage when the coelom is being formed. B, sagittal section of embryo in this stage. ', prototrochal cells. the hinder end of each streak there is, however, a compact mass which becomes hollowed out to form a coelomic vesicle, the rudiment of one of the pericardial sacs. The two meso- dermic bands then fuse together in the middle line behin
. Text-book of embryology. Embryology. IX MOLLUSCA 311 which span the blastocoele, extending from gut to ectoderm. In A _ „ B ph- Fig. 245.—Formation of the coelom iu Paludina mvipara. (After Brlanger.) A, optical frontal section of embryo in the stage when the coelom is being formed. B, sagittal section of embryo in this stage. ', prototrochal cells. the hinder end of each streak there is, however, a compact mass which becomes hollowed out to form a coelomic vesicle, the rudiment of one of the pericardial sacs. The two meso- dermic bands then fuse together in the middle line behind, and the pericardial sacs become pressed against one another so that their conjoined walls form a septum {sept, Fig. 247, B). Tonniges denies point-blank the existence of this ventral sac. According to him the adult mesoderm arises as an ectodermal proliferation, on each side of the middle line, which gives rise to the irregular mass of cells seen 0, transverse section in this stage, co^, coelomic poucli; (7, gut;. 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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