102 DUBLIN UNIVERSITY 



this genus, do not escape separately, but are emitted en masse, still in- 

 closed in the inner membrane of tho parent cell, within which, however, 

 they exert a vigorous movement, and involved still in which they settlo 

 down, and arrange themselves in a flat cluster, resembling that from one 

 cell of which they originated. But a more general increase by zoospores 

 has been attributed to the Desmidiacece, but I cannot find it corroborated 

 by direct observation that this actually takes place. • Certain it is that a 

 peculiar motion (or commotion) of the granular contents not uncommonly 

 occurs, and this more especially (in which my own experience confirms 

 Mr. Ralfs'), in specimens which have been kept some time in the house. 

 These minute moving bodies are apparently formed of the cell-contents 

 disintegrated and subdivided into an immense number of granular par- 

 ticles, and which exert an active, vigorous, tremulous, dancing kind of 

 motion, as if each one were elastic and perpetually meeting with some- 

 thing to make it rebound, and as quickly stopped only to meet with ano- 

 ther impulse, resulting in little or no actual change of position of the in- 

 dividual particles, notwithstanding all the commotion. I greatly fear this 

 fanciful description will hardly be intelligible ; indeed I think this peculiar 

 phenomenon thus attempted to be described must be witnessed to be com- 

 prehended. These moving granules have been assumed to be zoospores, 

 but the phenomenon may be due, possibly, to some sort of " molecular 

 motion." I have myself seen it in numerous genera and species. Mr. Ralfs 

 suggested that they (the agitated granules) are zoospores, and says they 

 occur when the cell approaches maturity. Dr. Carpenter calls them such, 

 and says they may be ciliated ; but without giving authorities. I have 

 seen this curious movement in cells undergoing division, and a3 active 

 in the young and as yet unformed segment of a frond during division 

 as in an old fully developed one. I have noticed, too, a precisely similar 

 movement in the germinating spore of an (Edogonium. To my eyes this 

 " swarming motion" does not resemble that of the true zoospores of 

 Cladophora, or of other Alga) which give birth to undoubted zoospores. 

 I have not seen anything to -indicate cilia, with only a J-inch object- 

 glass, however ; and for my own share I believe the nature or import 

 of this curious motion is undecided, and I should be glad, indeed, to 

 meet with any observations which would throw light on this phenome- 

 non, while, upon this point, as on many others, it would be as untrue, 

 as it would be unbecoming, to avow myself as not open to conviction. 

 I have before stated that the Desmidiaceae were formerly regarded 



