. Text-book of zoology for schools and colleges. Zoology. 112 INVEETEBKATE ANIMALS. of other animals. Thus the disease known as " hydatids " in the human subject is caused by the presence in his tissues of the cystic worms which are ultimately developed into the tape- worm of the dog. Okdek II. Tebmatoda. (Gr. trema, a pore or sucker).— The " suctorial" worms, or " flukes," as the members of this order are commonly called, are all internal parasites, inhabit- ing various situations in different animals, but especially af- fecting birds and fishes. They are all mor
. Text-book of zoology for schools and colleges. Zoology. 112 INVEETEBKATE ANIMALS. of other animals. Thus the disease known as " hydatids " in the human subject is caused by the presence in his tissues of the cystic worms which are ultimately developed into the tape- worm of the dog. Okdek II. Tebmatoda. (Gr. trema, a pore or sucker).— The " suctorial" worms, or " flukes," as the members of this order are commonly called, are all internal parasites, inhabit- ing various situations in different animals, but especially af- fecting birds and fishes. They are all more or less flattened and rounded in shape, and are furnished with one or more suckers, by which they adhere. They are distinguished from the Toeniada by always possessing an alimentary canal, which is often much branched (Fig. 40, 1), is simply hollowed out. Fig. 40.—Trematoda. 1. Dwloma TiepaUcwm^ the " Ijver-flute," showing the branched alimentary canal: 2. Anterior extremity of XHstoma lanceolatum^ enlarged; a An- terior sucker; & Posterior sucker; c Generative pore; (2 Gullet; e e Bifurcatiiig aliment- ary canal (after Owen). of the tissues of the body, and is never provided with a dis- tinct anus. The best known of the Trematoda is the common liver-fluke (Distoma hepaticum, Fig. 40, 1), which inhabits the gall-bladder or ducts of the liver in sheep, and is the cause of the disease known as the rot. In form it is ovate, flat- tened on the two sides, and presenting two suckers, of which the anterior is perforated by the aperture of the mouth. A branched water-vascular system is present, and opens pos- teriorly by a small aperture. The alimentary canal bifurcates shortly behind the mouth, the two divisions thus produced being much branched, and terminating posteriorly in blind extremities. In Distoma lanceolatum, (Fig. 40, 2) the intes- tine is divided into two branches, but these are simple tubes, and are not Please note that these images are extr
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