Miscellaneous. 2b'd 



On the Fore and Aft Poles, the Axial Differentiation, and a possible 

 Anterior Sensory Apparatus of Volvox minor. By Prof, J. A. 

 Rtdek. 



The Author remarked that he had recently had an opportunitv 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 Algse 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 

 coenobium. 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 

 coenobium impelled by the flagella of its cells projecting through its 

 envelope of cellulose. The direction of the rotation of the coenobia 

 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 Vol voces 

 leave their parent coenobium, which they do by breaking through 

 the wall of the latter at its hinder pole. 



The diameter of a Volvox-coenobium is slightly longer measured 

 along the axis around which it revolves than in the direction trans- 

 verso to it. It results from this that the coenobia 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 

 coenobium 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 detiiiite position in relation to the flagella and to the 

 axis around which the colony rotated. The anterior cells had the 

 brownish-red " eye-spots " largest ; and as one examined row after 

 row of the cells of the coenobium 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 



