. Principles of economic zoo?logy. Zoology, Economic. CLASSIFICATION 15 provided for them, where they decay. The animal matter in them is " beaten, squeezed, or washed out," and their skeletons sent to market (Fig. 9). Geographic Distribution.—Fresh-water sponges are found in streams and lakes in all the continents. Marine forms are found in all seas and in all depths, from the shore between tide-marks to the deepest abysses of the ocean. They are most abundant in tropical waters. Geologic Distribution.—Silicious sponges were not uncommon in the Cambrian Period, and are found in the
. Principles of economic zoo?logy. Zoology, Economic. CLASSIFICATION 15 provided for them, where they decay. The animal matter in them is " beaten, squeezed, or washed out," and their skeletons sent to market (Fig. 9). Geographic Distribution.—Fresh-water sponges are found in streams and lakes in all the continents. Marine forms are found in all seas and in all depths, from the shore between tide-marks to the deepest abysses of the ocean. They are most abundant in tropical waters. Geologic Distribution.—Silicious sponges were not uncommon in the Cambrian Period, and are found in the formations from. Fig. 8.—Bringing sponges from the vessels to sponge wharf at Key West. (Report U. S. F. C, 1902.) that time on. They were abundant in the Jurassic and very abundant in the Cretaceous of Europe; none have been found in that of America. Important Biologic Facts.—Even in this low type there is a differentiation of certain cells for certain purposes, as the skeletal and reproductive cells. True sexual reproduction ap- pears for the first time in the Porifera. Conjugation was noted in the Paramoecium. Classification.—Sponges are of three kinds: (1) The calcar- eous sponges, containing much lime. They are of little or. 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 Daugherty, Lewis Sylvester, 1857-; Daugherty, L. S. , Mrs. , 1859-. Philadelphia, London, W. B. Saunders
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