. Outlines of zoology. 2\iLtii xaaiisCiicK. - I. Ovum with germinal vesicle; 2, four-cell stage; 3. externalappearance of blastula; 4. blastula in section ; 5. beginning ofgastrula stage ; 6. section of completed gastrula. gut by a neurenteric canal, and to the exterior by theanterior neuropore (Fig. 254). The cavity of the gastrulaâthe archenteronâbecomesthe gut of the adult, and gives rise to the coelomic pouches. The notochord arises along the mid-dorsal line of thearchenteron ; its forward extension is secondary. During the early part of larval life the ectoderm cells,including those formi
. Outlines of zoology. 2\iLtii xaaiisCiicK. - I. Ovum with germinal vesicle; 2, four-cell stage; 3. externalappearance of blastula; 4. blastula in section ; 5. beginning ofgastrula stage ; 6. section of completed gastrula. gut by a neurenteric canal, and to the exterior by theanterior neuropore (Fig. 254). The cavity of the gastrulaâthe archenteronâbecomesthe gut of the adult, and gives rise to the coelomic pouches. The notochord arises along the mid-dorsal line of thearchenteron ; its forward extension is secondary. During the early part of larval life the ectoderm cells,including those forming the medullary canal, are this stage the larva is much more active than the adult. The later larvae are mqre sedentary, lying much on the 470 SUB-PHYLUM CEPHALOCHORDA. right side, and they are strongly asymmetrical. The mouthis placed at the left side; the gill-slits of one side appearconsiderably before those of the other; the primitive seg-ments of one side are not opposite those of the other, and.
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
