. Beginners zoology. Zoology. 26 BEGINNERS' ZOOLOGY ECTODERM CELLS INTERSTITAL 00 MUSCLE LAYER OVARY- OVUM scarce. Asexual generation (by budding) is common with the hydra when food supply is abundant. After the bud grows to a cer- tain size, the outer layer of cells at the base of the bud con- stricts and the young hydra is detached. Compare the sponge and the hydra in the fol- lowing respects: — many celled, or one celled; obtaining food ; breathing; tubes and cavities; openings; re- production ; loco- motion. Which ranks higher among the metazoa ? The metazoa, or many celled ani- mals, incl
. Beginners zoology. Zoology. 26 BEGINNERS' ZOOLOGY ECTODERM CELLS INTERSTITAL 00 MUSCLE LAYER OVARY- OVUM scarce. Asexual generation (by budding) is common with the hydra when food supply is abundant. After the bud grows to a cer- tain size, the outer layer of cells at the base of the bud con- stricts and the young hydra is detached. Compare the sponge and the hydra in the fol- lowing respects: — many celled, or one celled; obtaining food ; breathing; tubes and cavities; openings; re- production ; loco- motion. Which ranks higher among the metazoa ? The metazoa, or many celled ani- mals, include all animals except which branch ? Figure 39 is a mia'oscopic view of a vertical section of a hydra to show the structure of the body wall. There is an outer layer called the ectoderm, and an inner layer called the endoderm. There is also a thin supporting layer (black in the figure) called the viesoglea. The mesoglea is tlie thinnest layer. Are the cells larger in the endoderm or the ectoderm ? Do both layers of cells assist in forming the reproductive bud ? The ecto- derm cells end on the inside in contractile tails which form a thin line and have the effect of muscle fibres. They serve the hydra for its remarkable changes of shape. When the hydra is cut in pieces, each piece makes a complete hydra, provided it contains both endoderm and Fig. 39. — Longitudinal section of hydra (microscopic and diagrammatic).. 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 Coleman, Walter M. Toronto : Macmillan
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1921
