. A manual of zoology. 138 MANUAL OF ZOOLOGY. a proboscis. The mouth is never at the extreme anterior end, but is always ventrally placed, sometimes behind the middle. A few multiply by budding, and these may give rise to chains of individuals, which subsequently become separated. In the lowest Tur- bellaria the intestine is repre- sented merely by a nucleated mass of protoplasm ; in others it is a simple sac; in the major- ity it is branched. The general structure of the other internal organs very closely resembles that of the corresponding parts tt ° jj? in the Trematodes. Fig. 73. â pianar
. A manual of zoology. 138 MANUAL OF ZOOLOGY. a proboscis. The mouth is never at the extreme anterior end, but is always ventrally placed, sometimes behind the middle. A few multiply by budding, and these may give rise to chains of individuals, which subsequently become separated. In the lowest Tur- bellaria the intestine is repre- sented merely by a nucleated mass of protoplasm ; in others it is a simple sac; in the major- ity it is branched. The general structure of the other internal organs very closely resembles that of the corresponding parts tt ° jj? in the Trematodes. Fig. 73. â pianariapoiychroa (a), Turbellaria occur in the sea, lugitbris (<S), torva (c), about - , 1 , â 1 thrice the natural size. (After in iresh water, and also in damp Schmidt, from Claus.) .... . â,. localities on land. ihe great majority are non-parasitic, their food consisting of minute aquatic animals and plants of various kinds. An example is Planaria torva of our fresh-water pools and streams (Fig. 73, c). 3. THE CESTODA The class Cestoda or tape-worms are all internal parasites, and in the adult condition live in the enteric canal of verte- brates. The tape-worms are much more completely adapted to a life of parasitism than the Trematodes : they have no digestive system, and are nourished by the imbibition, through the general surface, of liquid nutriment derived from the digested food of the vertebrate host. The shape of a typical tape-worm is widely different from that of a trematode. A tape-worm (Fig. 74) is flattened like a trematode, but is extremely elongated, the length being. 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 Parker, T. Jeffery (Thomas Jeffery), 1850-1897; Haswell, William A. (William Aitcheson), 1854-1925. New York, The Macmillan Company; London, Macmillan & Co. ,Ltd.
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