The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . duct is physiologically a vagina. Lastlythe nervous system is well developed and consists of a pairof well-marked and interconnected ganglia placed near the anteriorend and dorsal to the oesophagus. From these ganglia, nerve-tractsprovided with ganglion-cclls are given off. Of these there are threeon each side of the body: a large ventral tract, smaller lateralstrands and dorsal ones. From these tracts a plexus of rierve-fibresis developed in connexion with the musculature and cuticle. The Tremato
The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . duct is physiologically a vagina. Lastlythe nervous system is well developed and consists of a pairof well-marked and interconnected ganglia placed near the anteriorend and dorsal to the oesophagus. From these ganglia, nerve-tractsprovided with ganglion-cclls are given off. Of these there are threeon each side of the body: a large ventral tract, smaller lateralstrands and dorsal ones. From these tracts a plexus of rierve-fibresis developed in connexion with the musculature and cuticle. The Trematodes are divided into three orders, primarily distin-guished by the character of their suckers, viz.: Hetcrocotylea,Aspidocotylea and Malacocotylea. Order i. Hcterocotylea.—Ectoparasitic Trematodes, in which alarge posterior adhesive apparatus is present and is usually accom-panied by a pair of suckers placed anteriorly in relation to the large posterior organ of attachment is usually wheel-shapedand provided with hooks; but the ridges may become separated 1 .!?.,-:\^ ,± T ^^-v:. Fig. 3.—Diagrammatic projections to show the relations of thefemale reproductive ducts; A, in the Malacocotylea; B, in theHcterocotylea. The ovary (a) leads into (6i) the oviduct, which isjoined at (g) by the duct of the yolk-glands {h). In B it is alsojoined by a paired vagina (t*^) and by the vitcIlo-Jntestinal duct (Laurers canal). /. (f) Shell-glands; (</) ootype; (0 uterus;(g) median-\iteno-duct; (i, i) intestine. 242 TREMATODES into a number ot independent suckers set on a disc or cotylo-phore. Eye-spots are general and the nervous system maintains aprimitive diffused condition. The excretory system opens to theexterior by a pair of dorsal pores at the level of the eggs are comparatively few, and development is direct, theembrjo after reachmg its host remaining attached to it for life. All the members of this parasitic on aquatic vertebratesand in rare case
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