Dr. CollingwooDj on Microscopic Alga. 89 



infinitesimal proportion of the scum upon those seas. I look 

 upon it as a species of Oscillatoria. 



The appearances presented by all these three forms under 

 the microscope are very similar, and the first two apparently 

 identical. The body, whether sheaf- or w'edge-shaped, is at 

 first opaque, but gentle pressure shoAvs each bundle to be 

 composed of a dense mass of cylindrical filaments of unequal 

 lengths, combined together and interlacing with each other, 

 forming an intricate network, having the aj^pearance of a 

 complicated basket-work with the ends of the osiers sticking 

 straight out, as Avhen the Avork is unfinished (fig. d). Each 

 filament is long, and beautifully symmetrical, unbranched, 

 with a rounded extremity, and perfectly even, hair-like out- 

 line. The filaments appear to be of equal diameter through- 

 out their entire length, and are filled with a dark-green 

 granular matter, which, before pressure is applied, renders 

 them nearly opaque, and prevents any examination of their 

 structure. 



The application of slight compression, however, renders 

 this form of the cells very evident, as well as their arrange- 

 ment in the filaments. Each filament apj^eared to be trans- 

 versely divided by delicate lines, as distinct in character as 

 the Avail of the filament, each cell being seen to contain some 

 granules of green matter in the interior, principally clustered 

 about the centre (fig. e). Every filament, then, Avas composed 

 of a linear series of tubular cells, and Avas, therefore, truly 

 jointed, like a Conferva, and not like an Oscillatoria, con- 

 tinuously tubular. I nowhere descried anything like an 

 empty tubule Avhich had discharged its contents bodily, nor 

 anything approaching to such an appearance, and, moreover, 

 further continued pressure, after rendering the cells more and 

 more distinct, ended by breaking the filament into distinct 

 cells, some of which presented a rectangular aspect, others a 

 round outline, according as they presented their sides or their 

 ends to view (fig. f). 



In neither of these forms did I cA-er notice anything Avhich 

 could be construed as a movement of oscillation, or indeed of 

 any kind. Neither was there visible any mucilaginous enve- 

 lope surrounding any of the specimens AA'hich I examined, 

 such as is so strongly insisted on by Ehrenberg in the speci- 

 mens obtained by him in 1823 in the upper part of the Red 

 Sea. 



As for the figures given by Montague in the ' Annales des 

 Sciences Naturelles ' (see fig. h), I can only say I cannot 

 recognise them as anything I noticed under the microscope. 

 Their irregular forms ofier a singular contrast to the symme- 



