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600 F. philippinensis. Wilson, in 1909, after a systematic study of the point in a considerable number of cases in Fiji, also considered that the local filaria was non-periodic— an observation amply confirmed by Bahr in 1910. Similarly, Fülleborn found that the micronfilaria of Samoa showed no periodicity. Strange to say, the filaria of neighbouring islands in the Pacific— namely, the Solomons, New Guinea, and the Bismarck Archipelago— are strictly periodic in their blood appearances.

Bahr has shown that the filaria of Indian immigrants who had acquired their filarial infections in India retain their periodic habits during at least three years of residence in Fiji, and that if an Indian or a Solomon Islander acquires the infection in Fiji the microfilarise are non-periodic in habit. Connal and Thiroux, in a proportion of instances of filarial infection in West Africa, have found the microfilarise to be non-periodic,* whilst in other instances they exhibit the nocturnal habit just as those of India, China, and America are known to do. As an explanation of this striking anomaly it has been suggested that the non-periodic microfilaria is the progeny of a parent worm specifically distinct from F. bancrofti; but Leiper has failed to find any difference between the Fijian mature worm and the F. bancrofti of India, China, and South America; and Fülleborn and Bahr, after minute study and comparison of the histology of the microfilariæ from those countries, find that they are identical in every respect. It may be, as Bahr suggests, that the non-periodic habit of the Pacific microfilaria is a partial adaptation to the day habit of its usual intermediary in Fiji Stegomyia pseudoscutellaris. (Plate XII.)

The subject of filarial periodicity, especially as regards the blood worms of the Pacific islands and West Africa, requires further study.

The mosquito the intermediary host of Filaria bancrofti.— Should the" females of certain