(1) This paper describes a new type of parasitic Protist, to which we have given the name Selenotnastix ruminantium (Certes). Its habitat is the rumen of Ruminants, especially that of the goat.
(2) The organism occurs in two chief forms--crescents and ovals. The crescents present a homogeneous, non-granular appearance, and possess a definite envelope; a single, large flagellum, conspicuous in life, arises from about the middle of the concavity of the crescent. The method of movement is variable; while the movement is sometimes effected by the flagellum, in other cases, perhaps more usually, it is produced by the body alone. In forward progression distinct antero-posterior polarity can be recognised. There is no properly constituted nucleus, the chromatin being present in the form of a peripheral layer, in which granules of varying size may occur, oi1 there tnay be one or two large masses projecting into the cytoplasm. Division is by equal binary fission, transverse to the long axis.
(3) The ovals resemble the crescents in general, but they never possess a flagellum, although capable of active movement. They show two types of minute structure : (A) ovals in which the chromatinic substance occurs as a narrow, peripheral layer, with or without granules in it. This arrangement agrees closely with that found in the crescents. (B) Ovals in the protoplasm of which two zones can be distinguished, a central, lighter-staining zone, comparable to the cytoplasm of (A) and of the crescents, and a peripheral, darker area of variable extent. This latter may be chromatinic in nature.
(4) We suggest that the second type of oval gives rise to the first type, and also that the crescent may pass into the first type of oval by the loss of the flagellum. We have no indication whether the crescents may be developed from the ovals or not.
(5) Apparently the only Flagellates from which this organism could be derived are theDinoflagellates, and, apart from the transverse division, there is no indication of any aflinity with this group. Further, the nature of the "nucleus" and the capacity of moving by. the body alone make it very doubtful if this parasite is a true protozoan.
(6) Selenomastix ruminantium differs in important respects from any known bacteria. It has no affinities with Schizo-saccharomycetes, with Blastocystis, nor with the Spirochaates. In certain characters it shows a resemblance to one or two large Spirillar forms, or to certain members of the Sulphur-Bacteria (e.g. Ophidomonas), but while its derivation is possibly to be sought in this direction, it is, nevertheless, very far removed from such forms. We may have in Selenomastix an example of a Pro-flagellate.
First real-time observation of transverse division in azooxanthellate scleractinian corals