131 



Newly- Observed Phenomena in the Conjugation of the 



Diatom Rhabdonema ar malum. 



By T. H. Buffham. 



{Read February 27th, 1885.) 



PLATES VII. & VIII. 



Before entering upon a description of the phenomena noticed 

 in the process of conjugation of this diatom, it will be instructive 

 to understand the peculiar structure of the frustule and habits of 

 the plant, for they undoubtedly govern the mode and circumstances 

 of that process which it is the purpose of the present paper to 

 describe. 



Rhabdonema arcualum grows in filaments which are attached to 

 marine algse. The filaments are of constant thickness, have 

 parallel sides, but differ from each other in breadth, being 3 

 to 9 times the thickness, so that the appearance is that of a 

 number of ribands. These filaments are found to contain from 

 2 to 60 frustules, but the frustule s themselves are not of equal 

 breadth (using this term now as extending along the direction of 

 the filament). Moreover, the breadths of the frustules are usually 

 different in the same filament. On taking the " front view " (as it 

 is called) of a frustule {i.e., in this instance the flatter side) the two 

 valves — one at each extremity — are seen to be separated by a con- 

 siderable distance from each other, the intervening space being filled 

 up by a number of annuli of the same length as the valves, and 

 equally siliceous. These will bear boiling in nitric acid without, 

 in many cases, separating. A few will, however, be found together 

 with free valves. A " side view " of a valve is shown on Plate VII., 

 Fig. I,x600. In Fig. 2 is drawn the same aspect (also x 600) 

 of an annulus. An extremely thin plate of silex is projected from 

 each extremity, but only from one side. It resembles, in fact, the 

 elliptical lid of a cardboard box with all the top removed excepting 

 a crescent at each end. To revert, then, to the frustule it will be 

 perceived that there are as many narrow chambers as annuli, all 

 freely communicating with the central large space, only that in 



