Miscellaneous. 253 
On the Fore and Aft Poles, the Avial Differentiation, and a possible 
Anterior Sensory Apparatus of Volyox minor. By Prof. J. A. 
RyvdER. 
The Author remarked that he had recently had an opportunity of 
studying a very large colony of Volvox minor, Stein, which appeared 
in the aquarium jars kept in the Conservatory of the Biological 
Department of the University of Pennsylvania. As some of the 
singular features of these Algee which he had noticed were appa- 
rently unrecorded, it was desirable that they should be described in 
order that others should have an opportunity of more fully investi- 
gating the facts and their bearings upon the life-history of these 
singular organisms. 
It. was noticed that there was an empty pole in every colony or 
ceenobium. ‘This empty or non-spore-bearing pole was always the 
anterior one, or that which was directed forwards in the act of 
locomotion, which is effected by a rotating motion of the whole 
ccenobium impelled by the flagella of its cells projecting through its 
envelope of cellulose. The direction of the rotation of the ccenobia 
is not constant and may be either sinistral or dextral; but the 
direction of progress always coincides with an imaginary axis passing 
through the centre of the anterior empty pole and the posterior 
germ-bearing portion of the nearly spherical colony or ccenobium. 
These poles are sometimes differentiated before the young Volvoces 
leave their parent ccenobium, which they do by breaking through 
the wall of the latter at its hinder pole. 
The diameter of a Volvox-ccenobium is slightly longer measured 
along the axis around which it revolves than in the direction trans- 
verse to it. It results from this that the ccenobia are somewhat 
smaller equatorially than axially, so that the form of the whole is 
that of a very slightly oblong spheroid. These characters are fairly 
constant and nearly always apparent, while that of the production 
of the spore in a little more than the posterior hemisphere of the 
ccenobium is invariable, as well as the uniform direction of the axis 
of progressive locomotion in relation thereto. 
Another very extraordinary fact which was observed was that 
the so-called “ eye-spots” found in the flagellate cells of the anterior 
pole of the spherical ccenobium were the largest, and invariably 
occupied a definite position in relation to the flagella and to the 
axis around which the colony rotated. he anterior cells had the 
brownish-red ‘ eye-spots ” largest ; and as one examined row after 
row of the cellsof the ccenobium in succession backward towards what 
one might term the caudal pole, these “ eye-spots’”’? were seen to 
gradually diminish in size, until in the last cells of the hinder pole 
they were barely distinguishable as minute reddish points, which 
elevated the protoplasm of the cells into a slight prominence, such 
as is more marked over the larger anterior “‘ eye-spots.” This re- 
markable fact of the ‘eye-spots” of the anterior pole being the 
largest revives in a striking way the query whether these reddish 
bodies are not really visual organs or sense-organs of some kind 
