2(52 CYCLOSIS AND BINARY DIVISION OF DESMIDIACEJE. 



to Closterium, having been seen in many other Desmidiacece. — An- 

 other curious movement is often to be witnessed in the interior of 

 the cells of members of this family, especially the various species 

 of Cosmariiun, which has been described as ' the swarming of the 

 granules,' from the extraordinary resemblance which the mass of 

 particles of Endochrome in active vibratory motion bears to a 

 swarm of bees. This motion continues for some time after the 

 particles have been expelled by pressure from the interior of the 

 cell, and it does not seem to depend (like that of true ' Zoospores ') 

 upon the action of Cilia, but rather to be a more active form of the 

 molecular movement common to other minute particles freely sus- 

 pended in fluid (§ 130). It has been supposed that the ' swarm- 

 ing' is related to the production of Zoospores (§ 190) ; but for this 

 idea there does not seem any adequate foundation.* 



202. When the single Cell has come to its full maturity, it com- 

 monly midtiplies itself by binary subdivision ; but the plan on 

 which this takes-place is often peculiarly modified, in order to 

 maintain the symmetry characteristic of the tribe. In a cell of 

 the simple cylindrical form of those of Didymoprium (Fig. 115), 

 little more is necessary than the separation of the two halves, which 

 takes place at the sutural line, and the formation of a partition 

 between them by the infolding of the primordial utricle, according 

 to the plan already described (§185) ; and in this manner, out of 

 the lowest cell of the filament a, a double cell b is produced. But 

 it will be observed that each of the simple cells has a bifid wart- 

 like j)rojection of the cellulose wall on either side, and that the half 

 of this projection, which has been appropriated by each of the two 

 new cells, is itself becoming bifid, though not symmetrically ; in 

 process of time, however, the increased development of the sides 

 of the cells which remain in contiguity with each other, brings up 

 the smaller projections to the dimensions of the larger, and the 

 symmetry of the cells is restored. — In Closterium (Fig. Ill, d), 

 the two halves of the Endochrome first retreat from one another at 

 the sutural line, and a constriction takes place round the cellulose 

 wall ; this constriction deepens until it becomes an hour-glass con- 

 traction, which proceeds until the cellulose wall entirely closes 

 round the primordial utricle of the two segments ; in this state, 

 one half commonly remains passive, whilst the other has a motion 

 from side to side, which gradually becomes more active ; and at last 

 one segment cpuits the other with a sort of jerk. At this time a 



undiscoverable when the greatest care is taken to avoid sources of fallacy. 

 I must confess to a similar scepticism respecting the external apertures 

 said by Mr. Osborne to exist at the extremities of Closterium ; for whilst 

 their existence is highly improbable on a priori grounds, Mr. Wenham 

 than whom no observer is entitled to more credit) states that "not the 

 slightest break can be discovered in the laminated structure that the 

 thickened ends display." 

 * See Archer in " Quart. Journ. of Microsc. Sci.,"Tol. viii. (I860), p. 215. 



