270 THE AMERICAN MONTHLY [Sept. 



tlie recession of the tide may be often found covered by 

 a brown film of similar living diatoms, not always of 

 the same shape, bat belonging to the same stage or pe- 

 riod in the life history of the diatom. In the autumn the 

 ditches of the salt marshes may be seen covered by a 

 thick film of floating algjie of a yellowish green or a 

 broA-nish color, frequently consisting chiefly of Oscilla- 

 ria (Oscillatoria), and containing vast numbers of active 

 spore- like organisms, of various shapes and sizes. Many 

 of these do not in the least resemble the diatoms in their 

 outlines, but are precisely similar to them in the color of 

 their endochrome and in the character of their motions, 

 and behave exactly like the above mentioned small dia- 

 toms when subjected to chemical treatment ; all alike be- 

 ing destroyed not only by acids and alkalies but also by 

 boiling water, and all alike also dissolve and disappear 

 when mud containing them is dried. I have no doubt 

 that all these represent the early stages in the growth of 

 diatoms from spores ; but my attempts to demonstrate 

 this by cultivation have failed, because I was unable to 

 protect them from their devourers, and give them sufli- 

 ciently natural conditions for their development. The 

 motions of the Oscillaria are very interesting, and show 

 some points of resemblance to those of diatoms. In 1889 

 in an article in this Journal, I pointed out the fact that 

 their proper motion was a revolution upon their axis, ad- 

 vancing or retrograding according to whether the revo- 

 lution was to the right or to the left. In all previous 

 accounts which I had seen their motion was described 

 as waving or nodding. Prof. Harvey in his " Nereis 

 Boreoli Americana," page 97, says, "These movements are 

 of three kinds : First, there is the oscillating movement ; 

 one end of the thread remaining nearly at rest, while the 

 other swags from side to side, sometimes describing 

 nearly a quarter of a circle in a single swing : Secondly, 

 the tip of the filament has a minute movement, bending 



