i897"9 8 -] Microscopic Life. 309 



Fragilaria capucina. It looks black in the water, but when a 

 number of filaments are dry and lying upon each other they 

 have a greenish metallic lustre. When mounted singly they 

 are nearly colourless and transparent. 



The organism to which we have devoted most time and 

 attention is the diatom Melosira varians. This is a filamentous 

 diatom which grows very profusely in the little pond at 

 Marchfield. We came across it very early in our investi- 

 gations, and were for a long time greatly puzzled as to its 

 nature. It grows out from the side-walls of the pond, ex- 

 tending to a distance of six inches or more. The filaments 

 are very fragile, so that it was not possible to say whether any 

 individual filaments extended to that length. We first sup- 

 posed it was a diatom because the endochrome is not green, 

 but yellowish brown of various shades, occasionally quite dark 

 brown. But we could discover no other characters of a diatom 

 in it ; and when at last we found it in fructification — the 

 cylindrical cells taking the form of perfectly round globes, 

 with two projections at opposite sides — we thought this was 

 a development that could not take place in a diatom, and that 

 the organism must therefore be an alga. On carefully and re- 

 peatedly looking through the plates in Cooke's book, we saw 

 nothing resembling the organism, although at one time we 

 thought it had some resemblance to an (Edogonium. At last 

 we found figures of Melosira varians and M. nummuloides in 

 the ' Micrographic Dictionary,' and of three species of Melo- 

 sira in Carpenter's book on the microscope. The latter show 

 the globes above-mentioned, and first gave us a clue to the 

 name. The organism seems well to deserve its specific name 

 of varians: the cylindrical filaments are of different breadth as 

 well as of different colours, the broader being as a rule the 

 darkest in colour ; and when first examined, it is somewhat 

 difficult to realise that they are cylindrical, as the cells look 

 like a series of brick-shaped bodies fastened end to end, and 

 there is no striation upon the outside, or other markings that 

 are usually found on diatoms. (Since writing the above, we 

 have once or twice seen slight striation ; but it is very faint, 

 and needs good illumination.) In the course of our investi- 

 gations, however, we frequently found the empty cells, some- 

 times broken, sometimes whole ; and when a broken fragment 



