Page:Tropical Diseases.djvu/853

XLIII] The parasite (Fig. 162).—The parasite itself is reddish brown in colour, thick and fleshy, and oval in form. So thick is it that its transverse section is almost round. It measures 8 to 16 mm. in length by 4 to 8 mm. in breadth, and is covered with broad scale-like spines. The anterior extremity is bluntly rounded and without cephalic cone; the oral sucker (Fig. 162, m) (0·88-1·12 by 0·80-0·83 mm.) terminal or sub-terminal; ventral sucker (Fig. 162, ac) (0·88-1·2 by 0·86-1·44 mm.) slightly larger than the oral sucker and situated somewhat anteriorly to the middle of the body. The pharynx is elongate, but the oesophagus is very short, so that the bifurcation of the intestine is considerably anterior



to the ventral sucker. The intestinal cæca (Fig. 162, i) run somewhat zigzag to the caudal end of the body. The genital pore opens close to the posterior margin of the ventral sucker. The testes (Fig. 162, t,t) are tubular, ramified, and situated on each side of the middle line, one slightly posterior to the other. The ovary (Fig. 162, o) is branched and is placed somewhat posteriorly to the ventral sucker, and either to the right or left of the middle line. The shell gland is lobate; the uterus (Fig. 162, ut) short and usually massed; the vitellaria (Fig.162, vg) are marginal and greatly developed.

For many years the mode in which this parasite entered man was unknown. Analogy suggested that the ova expectorated by the host were washed into water—rivers, ponds, wells, etc.—