AKCHER — ON STEPHANOSPHiEKA. PLTJVIALIS (COHN). 



which I brought before the Society, during last session.* Here the 

 contents of a single Mesotamium-cell escape therefrom without conjuga- 

 tion through a lateral or terminal or variously disposed opening, effected 

 by the raising up of a lid- or valve-like portion of the membrane of the 

 parent cell. During this act, the emerging contents are often much 

 constricted by reason of the narrowness of the aperture by which they 

 make an exit, and after emergence the mass becomes rounded. Now, 

 Mesotaenium is a plant which does not generate zoospores, and whose 

 developmental stages are regarded as quiescent, yet here the proto- 

 plasmic mass, wonderful as it may (at first sight) appear, actually comes 

 forth iuto freedom, through an opening very considerably smaller than 

 even the narrowest diameter of the former. This paradox is solved by 

 witnessing the phenomenon: — a lobe-like extension, I might write a 

 pseudopodal process, is protruded through the opening ; a portion of the 

 contents is slowly drawn after, thus relieving the mass behind, which 

 contracts upon itself ; and the gradual extension and expansion of the 

 portion outside the old membrane by degrees draws with it the whole ; 

 and its purpose, whatever it portend, is gained — that is to say, the whole 

 . protoplasmic mass and contents have acquired their freedom, and the old 

 parent-membrane is discarded and deserted. What immediately be- 

 comes of the "chlorophyll-plate" in this process I cannot say, but the 

 whole contents become more granular, in which I suppose the plate like- 

 wise takes a part ; or possibly it becomes consolidated in the centre, 

 causing the dark central spot in the spore-like body formed by the 

 emerged contents — it, at all events, affords no obstacle to a process 

 which at first sight, and until it is properly considered, appears almost 

 like a feat of legerdemain. 



Not to multiply examples, let us refer, lastly, to the modus operandi 

 of the process of conjugation in the genus Spirogyra. Two filaments 

 in juxtaposition about to conjugate put forth from opposite cells, as is 

 well known, short tubular processes, lined by a similar extension of the 

 "primordial utricle" bounding their contents. This indeed so far seems 

 to be only a process of growth, comparable to that which takes place in 

 a joint of Cladophora when about to give forth a branch, or to that of 

 the apex of the tubular filament of Vaucheria, &c. &c. But in the con- 

 jugating joints of Spirogyra, an actual contact and resorption of the in- 

 tervening septa having taken place, so as to produce an uninterrupted 

 connecting canal, there thereupon occurs a contraction of the cell-contents 

 of the conjugating joints. Presently one of these protoplasmic masses 

 passes over through the canal, to combine into a single spore with that 

 in the opposite cell. Now, the collective mass which is about to pass 

 over is actually of greater diameter than the transverse canal through 

 which it has to make its way. This, of course, can only be effected by a 

 process essentially similar to that which the cell-contents adopted or 

 underwent in the curious exceptional case in the Mesotaenium described 



* " Proceedings of the Natural History Society of Dublin," vol. iv., Part I., Plate I. 

 Figs. 21, 22, 23, 24. 



