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XLI] arrangement of the yolk cells in the female. Looss notices a greater development of the muscular system in the male S. japonicum, which he thinks may take the place of the absent cuticular eminences.

Catto found the adult worms in the smaller mesenteric blood-vessels, but he was unable to determine whether they occupy the arteries or the veins. He believes they occur in both. The smooth, non-tuberculated skin of S. japonicum seems to suggest a different anatomical habitat from that of S. hæmatobium, the integument of which is beset with numerous spine-bearing protuberances. S. hæmatobium, inhabiting the venous system, has a rough integument, it may be to enable it to adhere to the inner coat of the venules, and to stem the blood-stream during oviposition. S. japonicum, which inhabits the arteries, requires no integumental protuberances, the direction of the arterial current maintaining it in its proper position.

In Catto's case the ova were found chiefly in the mucous and submucous coats of the intestinal tract from cæcum to anus, more especially in the rectum and appendix. They were also found in the liver, in the gall-bladder, in the pancreas, in the mesenteric glands, and in the fibrous coat of the larger mesenteric vessels. In the liver they were very plentiful, lying singly or in clusters embedded in the hypertrophied connective tissue. The female schistosomum probably has a special means of extruding her eggs through the walls of the blood-vessels; the further distribution of the eggs being effected by the lymph-stream. Where the ova accumulate they provoke a small-cell infiltration, which gives place later to fibrous tissue.

The ova are discharged in the fæces of the vertebrate host. In this way they get carried to water, where the ciliated miracidium escapes. In 1913 Miyairi and Suzuki traced the ciliated miracidium into a fresh-water mollusc, Katayama nosophora (Fig. 143), wherein, after shedding its cilia, it becomes a sporocyst (Fig. 144, a), in which ultimately numbers of fork-tailed cercariæ are developed (Fig. 144, b). On maturity the cercariæ escape into the water and, opportunity presenting, penetrate the skin of some appropriate vertebrate (man, cat, dog, mouse, etc.), in whom they attain sexual maturity. These observations have been confirmed by Leiper.

Geographical distribution.—The distribution of S. japonicum is probably a wide one. So far it has been found principally in Chinese and Japanese. It is far from uncommon in the Philippines, or in the Yangtze valley, where a notable