Microscopical Society. 311 
MICROSCOPICAL SOCIETY OF LONBON. 
Oct. 21, 1840.—Richard Owen, Esq., President, in the Chair. 
A communication from the Rev. C. G. Vernon Harcourt to Mr. 
Owen was read, in which the author relates his observations made 
upon some microscopic animalcules found in a pond at Nuneham. 
The author’s attention was attracted to the subject by observing 
the brilliant masses of red which appeared in the pond in the morn- 
ing, and seemed to disappear in the evening. Portions of this were 
collected and submitted to the microscope. It was found to consist 
of a number of small particles adhering together so as to form a con- 
tinuous film, which floated upon the surface of the water in the 
glass in which it was kept, but after a few hours resolved itself into 
its component particles, which sunk to the bottom. 
When the films were observed in the pond they were found to be 
of a green colour until six o’clock in the morning, at which hour 
they begin to change from green to red. The red colour continues 
until four o'clock “in the afternoon, at which hour the films, after 
passing through shades of brownish purple, again return to the 
green state, and so continue until the following morning, when the 
same phenomena are repeated. 
It was found very difficult to keep the animals in their green 
state, and the only good opportunity of examining them in that con- 
dition was found to be by the side of the pond. When carried home 
in a wine-glass they quickly became red. Some, however, were col- 
lected, with great care not to disturb them, in a wash-hand basin, 
which was left in the open air. The films remained united and went 
through their regular changes for three days, after which the crea- 
tures fell to the bottom, remained red, and appeared dead. 
The change of colour from green to red, and vice versd, appears 
to depend on certain alterations taking place in the interior of the 
animal. Although the mass of united animals looks green, yet there 
may always be discovered with the microscope, in each individual, a 
red spot, which when the mass becomes red dilates, the animal 
being stretched out at full length, with the mouth and vent open. 
The green colour is reproduced by the red interior contracting to- 
wards a vent near the tail. The process by which these changes 
are effected was repeatedly observed. 
The animals were never observed to feed, nor was anything ejected 
from the vent. ‘They are very sluggish, and when separated were 
never seen to reunite. Ina cloudy morning they are of a purplish 
brown colour, the dilatation of the red interior not being completed, 
and when it rains they sink to the bottom. 
The author refers to the figure in Shaw’s Miscellany of Cercaria 
mutabilis (muiabilis, from change of shape, not of colour) as furnishing 
a correct representation of most of the appearances which the ani- 
malcule assumes in its red state, and offers some conjectures as to 
the possibility of Shaw having mistaken the different appearance of 
the animal at different times as indicative of a difference in species. 
