192 
One of our Common Monads. 
in either the larger or the smaller groups, nor do I believe that any 
such membrane exists in any true species of Urella. 
I was able to distinguish clearly two flagella, both arising from 
a point near the most elevated side of the base of the cone. The 
larger one was stiff, arcuate with the concave side toward the base 
before mentioned, somewhat longer than the body of the Monad, 
and very plainly seen with any objective above a J-inch ; the 
smaller is very delicate, short, and incessantly active. I first saw 
it with a Wales’ T Vth ; but after becoming familiar with its appear- 
ance, I was always able to detect it with a Tolies’ |th or a Hartnack 
No. 9. 
I am not certain as to the number of contractile vesicles, but it 
is my opinion that there is but one: sometimes a larger number 
of clear spaces would be seen in the body, but they were not 
observed to contract. I do not wish, however, to speak with any 
degree of positiveness upon this point, as I was not able to keep a 
single Monad in view long enough to satisfy myself, on account of 
the constant revolution of the colonies. As regards the ingestion 
of food, I have seen something, though not as much as I could 
wish, as this is still a disputed question. I fed them with indigo, 
which they ate readily, and I frequently watched its ingestion. On 
account of their incessant motion, I was not able to satisfy myself 
of the existence of a definite mouth, but I did not see a single 
instance of the indigo being received at any point except very near 
the common base of the flagellum, and in every instance observed 
the act of ingestion was preceded by a quick bending of the larger 
flagellum, by which the particle of indigo was thrown against the 
surface of the body in a manner similar to that described by Pro- 
fessor Clark in his observations upon Monas. So far as I was able 
to follow the process, whenever a colony reduced its rate of motion 
sufficiently to permit of careful observation upon this point, it was 
so much like the process described in Monas as to leave little doubt 
in my mind that it was substantially the same, although, as I have 
said, I did not see a distinct mouth. 
It appears probable, now that the Monadina are better under- 
stood, that we shall soon be able to recognize in them a well-defined 
family of the Flagellate Infusoria, although, doubtless, many forms 
that have been assigned to that group are vegetable in their nature. 
These will be gradually removed, and those forms which are un- 
questionably animal will be distinguished. Among these it seems 
to me the genus Urella, as described by Ehrenberg, will undoubt- 
edly take its place. — A paper communicated to the Section Micro- 
scopy of the Boston Society of Natural History. 
