. The animals and man; an elementary textbook of zoology and human physiology. Zoology; Physiology. THE INVERTEBRATES 133 islands on which men live; others live parasitically in our bodies to our great discomfort and danger; many are per- sistent enemies of our crops and domestic animals. Finally, all in their structure, their physiology, their development and growth, their extraordinary adaptations to the con- ditions of their life, their marvelous modes of distribution, their beauty of color and pattern, and symmetry of outline, appeal to that inborn love of knowledge in us, as subjects to s
. The animals and man; an elementary textbook of zoology and human physiology. Zoology; Physiology. THE INVERTEBRATES 133 islands on which men live; others live parasitically in our bodies to our great discomfort and danger; many are per- sistent enemies of our crops and domestic animals. Finally, all in their structure, their physiology, their development and growth, their extraordinary adaptations to the con- ditions of their life, their marvelous modes of distribution, their beauty of color and pattern, and symmetry of outline, appeal to that inborn love of knowledge in us, as subjects to study, admire and enjoy. Sponges.—^A bath or slate sponge is simply the skeleton, or part of it, of a sponge animal. In life all of this skeleton is in- closed or covered by a soft, tough mass of sponge flesh. Sponges are fixed, ex- cept when very young, when they swim frpely about. They are found at all depths and in all seas, grow- ing especially abun- dantly in the Atlan- tic Ocean and the Mediterranean. A very few kinds live in fresh water, being found in lakes, rivers, and canals, in all parts of the world. The shape of the simplest sponges is that of a small vase, or nearly cylindrical cup, attached at its base, and having at the free end a large' opening (fig. 53). But most sponges are very unsymmetrical and grow more like a low, compact, bushy plant than like the animals we are familiar with. The smallest sponges are only I mm. (1-25 in.) high, while the largest may be over. Fig. S3. A simple sponge, Granlia sp.; at right a longitudinal section, showing the simple body-cavity. (One-half natu- ral size; after Jordan and Kellogg.). 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 Kellogg, Vernon L. (Vernon Lyman), 1867-1937; McCracken, Mary Isabel. New York, H. Holt and Company
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