220 ARCHER, OX DESMIDIAI E 1 '.. 



of more general occurrence in specimens for some time kej 

 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 disintegrated endochrome, broken up into an immense 

 number of exceedingly minute non-ciliated granular particles, 

 at once innumerable and, I apprehend, immeasurable. Not- 

 withstanding all the commotion, there is no very great change 

 of place in the active granules themselves. They not unfre- 

 quently form a dense cluster together, so crowded as to ap- 

 pear 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 repre- 

 sent this in Fig. 1) ; but shortly thes 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 algre, and in germinating 

 spores, which had already commenced to elongate. Amongst 

 the Diatomacepe (in Epithemia turgida, and in a species of 

 Cymbella), I have seen the endochrome throughout the frus- 

 tule to each extremity entirely disintegrated into nearly equal 

 and extremely minute and free particles, and these exerting a 

 very vigorous, tremulous, dancing movement, perfectly iden- 

 tical 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 Rev. E. O'Meara in Pleurosigma 

 Spencerii — (vide Proceedings of last session, 'Nat. Hist. Rev.,' 

 vol. v, p. 192), alluded to, however, as anthozoids, but more 

 probably zoospores), and in Epithemia Argits, E. gibba, and 

 Cocconeis pediculus, at our last meeting. A similar movement 

 of the ultimate granules, which appear brown and quite dead 

 in various organisms, is sometimes noticeable. This, then, in 

 all such examples I should be inclined to imagine is a mani- 

 festation of the phenomenon called " molecular movement," 

 similar to that noticeable in the granules of the ibvilla of 

 pollen in the flowering plants, or to that Been whim a small 

 portion of the substance of the common fresh-water sponge 

 is crushed down and viewed under the microscope and of this 

 other examples might be cited), and rather in the eases so 

 common in the Desmidiaceae, and in the very rue examples 

 referred to in the Diatoniaeea 1 , indicative of decay, than as 

 the precursor of a further developmental change. I do not, 

 of course, include the singular movement of the free, active 

 particles at the extremities of Closterium, Docidium, \c, 

 \,!iieh, as every specimen of the species in which it occurs 



