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210 separable from the group of the Achlyæ, or, rather, from a group which embraces Achlya, Empusina, Sporendonema and possibly Botrytis, all being members of the Protista group, whose natural distinctions, evident enough sometimes, are not so in some parts of their life-cycle. That one becomes the other, on a change of the surrounding medium occurring, is one of the most interesting and suggestive of facts. Evidently the parasite got into the old corals, as it does into those now living, from the outside, and by contact, growth, pressure, protoplasmic movement and the dissolving effect of the evolved gas, slowly and surely penetrated. The course, size, shape, and length of the tube being determined by the presence of the organic matter within the sclerenchyma and the arrangement of the coral-spicula, it is best to term the entophyte an Alga, and to classify it amongst the unicellular types in the neighbourhood of Achlya, calling it Palæachlya perforans. It is of course important to decide when the perforations were made. Were they forming contemporaneously with the growth of the coral and shell, or were they of subsequent date? In the first case the Silurian and Devonian age of the Achlyan becomes apparent; but if the second supposition be at all consistent with facts, the whole interest of the subject vanishes.

In favour of the theory of the simultaneous life of the host and the parasite, the theory of the growth of the Algæ in recent times must be advanced and the presence of sea-water and of animal tissue of a low vitality assumed. In addition there is the fact that a portion of a Brachiopod included in a sandy matrix within the coral, and not continuous with coral-structures, contains the tubes. Moreover the crystalline mass of the interstices of the coral, although it holds mechanically abundance of spores, does not present tubes or any evidence of growth. It is therefore in accordance with our knowledge to assert that the parasites lived at the same time as the organisms which they penetrated, and that this minute Alga presents one of the most singular proofs of the persistence of form and life-cycle from the palæozoic age to the present. In conclusion, I have to thank Mr. W. S. Dallas, Prof. Morris, and Mr. H. Woodward for references, suggestions, and sections.

The characteristic tubes of this Alga have been found by me in species of Cyathophyllum from the Upper Silurian, and in a Foraminifer from the Lower Silurian of Canada.

Fig. 1. Tubes in Thamnastæa from the Miocene of Tasmania, × 350.

2. Tubes in Goniophyllum pyramidale from the Upper Silurian, close to the wall, × 350.

3. Spores in Goniophyllum pyrarnidale, × 450.

4. Tubes in the shell of a Brachiopod imbedded in Goniophyllnm pyramidale, x 350.