DUBLIN NATimAL HLSTORT SOCIETY. 25 



Niigeli; also Al. Braun's "Algarum Unicellularium Genera nova et 

 minus cognita," where I learn that the views of Nageli and Braun were 

 identical with the conclusions that had forced themselves on myself, and 

 that those distinguished algologists had actually long since seen fit to 

 remove Pediastrum and its allies from Desmidiaceae, and have trans- 

 ferred them meantime to the somewhat more humble family, Pal- 

 mellacese. 



"While, then, the object of this paper is to prove that what I think 

 must be looked upon as zoospores do occur in at least one species in this 

 family, and, therefore, may occur thi-oughout, and that our books are 

 therefore not wrong in assuming it (leaving Pediastrum out of the ques- 

 tion), still I am inclined to think, as I before indicated, that the state- 

 ments alluded to are founded rather on the occurrence of what I am 

 disposed to imagine a distinct, but, perhaps, more unaccountable phe- 

 nomenon, than on any published record of what can be looked upon as 

 true zoospores, Pediastrum excepted. I allude to what has been called 

 the "swarming movement" of the ultimate granules of the cell-contents, 

 a phenomenon of common occurrence ia this family. Indeed, I believe 

 I have myself noticed it more or less frequently in nearly every species 

 I have seen, and even in those undergoing division. It seems of more 

 general occurrence in specimens for some time kept in the house ; yet, 

 frequent as it is, it is difficult to describe, and almost requires to be seen 

 to be understood. It consists of an active, tremulous, vibratory, dancing 

 kind of motion of the disiategrated endochrome, broken up into an im- 

 mense number of exceedingly minute non-ciliated granular particles, at 

 once innumerable, and, I apprehend, immeasurable. ^Notwithstanding 

 all the commotion, there is no very great change of place in the active 

 granules themselves. They not unfrequently form a dense cluster to- 

 gether, so crowded as to appear a black mass. Sometimes I have seen 

 these masses of active granules abruptly bounded on one side by a 

 straight line, as if there were some invisible barrier preventing their 

 assuming a more scattered appearance (I have tried to represent this in 

 Fig. 1 ) ; but shortly this abrupt line becomes broken, and the cluster 

 loses this appearance, and becomes gradually thinner. I have noticed 

 a very similar movement, though less active, in various other algae, and 

 in germinating spores, which had already commenced to elongate. 

 Amongst the Diatomaceae (in Epitliemia turgida, and in a species of 

 Cymbella), I have seen the endochrome throughout the frustule to each 

 extremity entirely disintegrated into nearly equal and extremely mi- 

 nute and loose particles, and these exerting a very vigorous, tremulous, 

 dancing movement, perfectly identical with what is alluded to in the 

 Desmidiaceae, and, so far as I can see, in no way to be mistaken for the 

 movement of the bodies described by the Eev. E. O'Meara in Pleuro- 

 sigma Spencer ii — (vide Proceedings of last session, Nat. Hist. Rev., 

 vol. v., p. 192, alluded to, however, as Anthozoids, but more probably 

 Zoospores), and in Epithemia argus, E. gihha, and Cocconeis pedi cuius, 

 at our last meeting. A similar movement of the ultimate granules, 

 which appear brown and quite dead in various organisms, is sometimes 



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