. Animal biology. Zoology; Biology. 130 METAZOAN PHYLA In the rhagon type the animal is much larger and the whole body forms a rather thick mass penetrated by a complexly branched canal system. In the fresh-water sponges, which may be taken to represent this type, the ostia lead into subdermal cavities. From these cavities incurrent canals run to chambers lined with flagellated cells. After the water has passed these flagellated cells it is carried by excurrent canals into a gastral cavity, which opens to the outside by an osculum. 152. Skeleton.—The classification of the sponges depends upon
. Animal biology. Zoology; Biology. 130 METAZOAN PHYLA In the rhagon type the animal is much larger and the whole body forms a rather thick mass penetrated by a complexly branched canal system. In the fresh-water sponges, which may be taken to represent this type, the ostia lead into subdermal cavities. From these cavities incurrent canals run to chambers lined with flagellated cells. After the water has passed these flagellated cells it is carried by excurrent canals into a gastral cavity, which opens to the outside by an osculum. 152. Skeleton.—The classification of the sponges depends upon the character of the skeleton, which may be made up of spongin or of spicules. The spicules may be either calcareous or siliceous and differ in shape in the different forms. Spongin is a substance which chemically is similar to silk and which is formed by cells known as spongoblasts. Spicule- Oscu/a/^ Oscu/um. Rac//(f/ ccrncf/ chamber Incurrent \/y^ '^ Oscu/un? ?^ ^ Gcistral cav/'-f-y. 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 Wolcott, Robert Henry, 1868-1934. New York ; London : McGraw-Hill Book Company, Inc.
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