. Animal activities; a first book in zoo?logy. Zoology; Animal behavior. ONE-CELLED ANIMALS AND SPONGES. 123. *iouth for taking food and the two kinds of cilia, one for locomotion and one for producing currents of water to drive food into the mouth. Even a single cell then may have its parts specialized for per- forming different kinds of work. Characteristics of tlie Protozoa. The Protozoa are minute animals having but a single cell of protoplasm, moving by pseudopodia, or cilia, and reproducing withouteggs. Sponges. Itis not rec- ommended that sponges be studied in the labora- tory in an ele
. Animal activities; a first book in zoo?logy. Zoology; Animal behavior. ONE-CELLED ANIMALS AND SPONGES. 123. *iouth for taking food and the two kinds of cilia, one for locomotion and one for producing currents of water to drive food into the mouth. Even a single cell then may have its parts specialized for per- forming different kinds of work. Characteristics of tlie Protozoa. The Protozoa are minute animals having but a single cell of protoplasm, moving by pseudopodia, or cilia, and reproducing withouteggs. Sponges. Itis not rec- ommended that sponges be studied in the labora- tory in an elementary course, but for purposes of comparison it is neces- sary to become familiar with the most important facts concerning their structure. Sponges are composed of many cells but slightly specialized. A single sponge really seems almost as much like a colony of Protozoa as like a distinct animal. The outer layer of cells which is simply a sort of skin is called the ectoderm; the inner layer or lining of the cavities of the body is called the endoderm. Between the ectoderm and the endoderm lies the mesoglcea, in which the skeleton is produced. The flesh of the sponge taken altogether is called sarcode. The com- mon bath-sponge as we use it is only the skeleton. We may imagine that the hard parts we see have once been imbedded in fleshy matter (mesoglcea); that the fleshy matter was covered with a skin (ectoderm); and that the cavities so apparent in the skeleton were lined with another skin (endoderm). Fig. 107. — A Paramecium {highly magnified). , oral groove; ///, 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 French, Nathaniel Stowers, 1854-. New York [etc. etc. ] Longmans, Green and Co
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