185^5.] MICROSCOPICAL JOURNAL. 271 



from side to side, like the head of a worm, and, thirdly, 

 there is an onward movement, probably the result of the 

 two former." As the filament has a rigid sheath of cel- 

 lulose it must be credited with an extraordinary muscu- 

 lar development if it was able to bend the tip "from side 

 to side like the head of a worm." A closer examination 

 would have shown that the tip was rigidly bent to one 

 side, and that the change in position was caused by the re- 

 volving motion, forcing it forward in a spiral path through 

 the water. The waving motions are caused by tension ; 

 the elacticity of the filament causing it to spring out 

 when working itself free from obstructions. 



The desmids also resemble the diatoms in some par- 

 ticulars, and have a peculiar motion not often seen ; some 

 of them move end-ways like the oscillaria, the Closterium 

 fastens one end and then swings the other around 

 abruptly, sometimes describing a half circle in one 

 swing; the Micrasterias, Cosmarium and Euastrum 

 have a peculiar jigging motion, waddling along like a 

 duck, as if they were advancing on two short legs placed 

 near their centers. The natural habitat of both desmids 

 and oscillaria is in fresh water, but the oscillaria are 

 found in abundance in the ditches of the salt marshes ; 

 these ditches are sometimes very nearly fresh, but cer- 

 tain marine organisms appear to accommodate them- 

 selves to the change, and some species of marine diatoms 

 are found far up the rivers where the water is entirely 

 fresh, and certain species of oscillaria are found most 

 frequently in water that is more or less salt. Spirulina 

 tenuissima is frequent in the ditches of the marsh between 

 Morris Creek and South End. This variety has the most 

 rapid revolving motion of any that I have observed, 

 making two or three revolutions each second ; but its 

 onward progress does not correspond in rapidity with 

 the rate of revolution. In these ditches, and also in 

 Morris Creek, I find a very large variety that I have 



