AllCHElt, OX DESMIDIACE.E. 



223 



the rupture of the cell- wall, aud of which every one may 

 develop into a new cell. These ' gonidia' may be endowed 

 with cilia, and many possess an active power of locomotion, 

 in which case they are known as ' zoospores ;' or they may 

 be destitute of any such power, and may become en- 

 closed in a firm cyst or envelope, that seems destined for 

 their long- continued preservation, in which case they are 

 designated as ' resting spores.' — The movement of the zoo- 

 spores, first within the cavity of the cell that gives origin to 

 them, and afterwards externally to it, has frequently been 

 observed in the various species of Cosmarium, and has been 

 described under the title of the ' swarming of the granules/ 

 from the extraordinary resemblance which the mass of moving 

 particles bears to a swarm of bees. The subsequent history 

 of their development, however, has not been fully traced out ; 

 and this is a point to which the attention of microscopists 

 should be specially directed." With great diffidence, I 

 venture to suggest that the statements in the foregoing 

 passage must be based on the swarming movement of the 

 minute granules which I have endeavoured to describe above. 

 I am disposed to believe that the granules which the author 

 terms gonidia are not ciliated; and, although the species 

 of Cosmarium often show the movement, it is by no means 

 confined to that genus, but may be frequently seen also in 

 multitudes of other species. The author then goes on to 

 describe the formation of undoubted zoospores in Pediastrum. 

 As to " resting spores," I imagine he must allude to such 

 bodies as are figured by Ralfs in Desmidium Swartzii (' Br. 

 Des./ tab. iv, f.), where they are not produced by conjuga- 

 tion, but seem to be due to the consolidation of the contents 

 of each individual joint, which becomes enclosed in its own 

 special envelope, as sometimes takes place in Spirogyra, 

 &c. Braun suggests that the filament met with by Ralfs 

 may have been one which had entered into conjugation with 

 another filament, and that the string of empty cells had been 

 torn away; but this is certainly not the case, for I have 

 myself met with the species in question in some abundance 

 in precisely the same condition as that figured by Ralfs, 

 and which consist in the cell-contents of a greater or less 

 number in immediate succession of the cells of certain fila- 

 ments becoming retracted to the centre of the cavity of each 

 cell, and becoming there massed together into a definitely 

 bounded spore-like body, without any process of conjugation 

 or union of the contents of distinct cells. But I was not 

 able to see any further development, and the specimens soon 

 died. {Vide also, for resting-spores (?) ' Micrographic Die- 



