. Animal studies. THE WORMS 61 season, and at such periods they may be found moving about with a steady gliding motion (due to cilia covering the en- tire body), varied occasionally by a looping, caterpillar move- ment, or by swimming with a napping of the sides of the body. When watched at such times they may sometimes be seen to snatch up small worms, snails, small crabs and insects, which serve as food. More closely examining one of these forms, for example, the species usually found on the under side of sticks and stones in our shallow fresh-water streams (Fig. 32, A), we note that the for
. Animal studies. THE WORMS 61 season, and at such periods they may be found moving about with a steady gliding motion (due to cilia covering the en- tire body), varied occasionally by a looping, caterpillar move- ment, or by swimming with a napping of the sides of the body. When watched at such times they may sometimes be seen to snatch up small worms, snails, small crabs and insects, which serve as food. More closely examining one of these forms, for example, the species usually found on the under side of sticks and stones in our shallow fresh-water streams (Fig. 32, A), we note that the forward end is not developed into a well-defined head as in the higher worms, but is readily determined by the presence of very simple eyes and tentacles, while the lower creeping surface is dis- tinguished by a lighter color and the presence of the mouth. Through this small opening a slender proboscis (in reality the pharynx) may be extended some distance, and may be seen to hold the small organisms upon which it lives until they are suffi- ciently digested to be taken into the body. 54. Digestive system.—In the smaller flatworms, some of which are scarcely larger than many of the Protozoa, the alimentary canal is a sim- ple unbranched tube; but in the larger forms such an ap- paratus is replaced by a greatly branched digestive tract which furnishes an extensive surface for the rapid absorp-. -Anatomy of fresh-water flat- worm (Planaria). exs, escretory sys- tem, with flame-cell (/). The ali- mentary canal is stippled. B, nerv- ous 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 Jordan, David Starr, 1851-1931; Kellogg, Vernon L. [from old catalog].
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Keywords: ., bookauthorjordanda, bookcentury1900, bookdecade1900, bookyear1903
