NATURAL HISTORY. 67 
such weather they come to the surface, but, 
when the atmosphere is cloudy, they remain on 
the sediment at the bottom of the trench or 
pond —a circumstance which renders them 
dificult to be procured. When found at the 
bottom, they congregate in clusters, and, to the 
unassisted eye, resemble short filaments of 
vegetable matter, interwoven with each other. 
As their motions are slow, they may easily be 
mistaken for a mass of decayed weed. They 
may be preserved alive for several months in a 
glass vase, where their habits can be observed 
without disturbing them, and, when plentifully 
supplied with food, they rapidly increase in 
numbers and size. They do not undergo any 
transmutation. Those I caught in June were 
about two-tenths of an inch when extended, 
and about half that length in a contracted 
state. The vase in which they were kept held 
about three quarts, and was well supplied with 
small monoculi (Daphnia and Lyncei, Miiller.) 
In October, four months after they were caught, 
they had become exceedingly numerous, and 
they congregated together in large masses, and 
many of them measured six-tenths of an inch 
when extended. Several of the larger ones, 
when examined under a microscope, had nume- 
