210 P. M. DUNCAN ON SOME UNICELLULAR ALG.E 



separable from the group of the Achlyce, 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 en\tophyte an Alga, and 

 to classify it amongst the unicellular types in the neighbourhood 

 of Achlya, calling it Palceachlya perforans. It is of course im- 

 portant 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 Algae 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, con- 

 tains the tubes. Moreover the crystalline mass of the inter- 

 stices 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 

 palaeozoic 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 CyathophyUum from the Upper Silurian, and in a 

 Foraminifer from the Lower Silurian of Canada. 



EXPLANATION OF PLATE XV. 



Fig. 1. Tubes in Tkamnastraa from the Miocene of Tasmania, X 350. 



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



the wall, X 350. 



3. Spores in Goniophyllum pyrarnidale, X 450. 



4. Tubes in the. shell of a Brachiopod imbedded in Goniophyllnm pyra- 



rnidale, x 350. 



* See Micrographic Dictionary. 1875, 3rd edit, for these genera. 



