152 NATURAL HISTORY SOCIETY OF DUBLIN. 



nization and development of this plant, such as the macro- and microgo- 

 nidia, &c. As regards the latter, nothing further presented itself as to 

 the purport or function of the bodies so called — like Cohn's own original 

 specimens, they were formed, and disappeared. 



This gathering was extremely free from other organisms. CJilamy- 

 dococcus pluvialis did not present itself, thus, in that respect, unJike 

 Cohn's original supply. A very few specimens, however, of Goniumpec- 

 torale occurred, but in so trifling numbers, that for a fortnight after I 

 obtained the material, I do not believe I noticed half-a-dozen indivi- 

 duals, while the Steplianosplmra existed in myriads. The only exam- 

 ples of animal life to be noticed were a very few lively specimens of a 

 noble rotiferon, a Brachionus. 



However, before drawing attention to the peculiar condition alluded 

 to, a very brief description of the organism in question may not be out 

 of place, indeed such would perhaps be of advantage, if not essential (in 

 the absence of a previous study of Professor Cohn's extended memoirs), 

 to the appreciation of the confessedly imperfect observation which it is 

 the object of this paper to communicate, and which indeed is the only 

 new one I have to note, that has not been recorded by Cohn ; and in 

 doing so, I shall not enter into minute details beyond those which bear 

 directly on the subject of this note. 



The Family of Chlorospermatous Alga?, Volvocinacese, to which this 

 plant belongs, is characterized by the individual green cells, being, dur- 

 ing the greatest part of their life, active zoospore-like bodies, ciliated, 

 either solitary or combined into definite groups, and either with a com- 

 mon enveloping membrane, until breaking up in carrying out vegeta- 

 tive developmental processes, or without a common membrane. With 

 the exception of the genus Protococcus (Chlamydococcus) which is a 

 single cell, the cells, though thus for the greater part of their existence 

 associated into colonies, maintain their special physiological indivi- 

 duality ; and collectively, at the same time, represent but one individual 

 in relation to external objects. With these general characters, Stepha- 

 nosphaera accords ; that is to say, it consists of families of ciliated cells 

 which originate from a single mother-cell through a series of divisions 

 following a definite law ; and when completed, the family possesses its 

 own characteristic collective figure and organization. Here there are 

 eight green masses of protoplasm — "primordial cells" (Cohn) — arranged 

 circularly at regular intervals within a common hyaline membranous 

 globe, so as to form an equatorial series. Each primordial cell is fur- 

 nished with a pair of fiagelliform cilia, which protrude through the hya- 

 line globe, and, by their action in the surrounding water, cause the ac- 

 tive revolution hither and thither of the aggregate family, that is, of the 



also Colin and Wichura, " Ueber Stephanosphsera," Kais. Leop.-Car. Akademie der Na- 

 turforscher ; Bonn, 1857. Of the latter memoir there is a short abstract in the " Quart. 

 Journ. of Microscopical Science," vol. vi., p. 131. 



