256 MICROSCOPIC FORMS OF VEGETABLE LIFE. 



take in a large part of the cavity of the cell, so that the colored 

 contents seem only like a deposit on its walls. Before long, this 

 "motile" primordial utricle acquires a peculiar saccular invest- 

 ment, which seems to correspond with the cellulose envelope of 

 the "still" cells, but which is not so firm in its consistence (i, K, 

 L). Thread-like extensions of the protoplasm, sometimes con- 

 taining colored globules, are not unfrequently seen to radiate 

 from the primordial utricle towards the exterior of this envelop- 

 ing bag (i) ; these are rendered more distinct by iodine, and can 

 be made to retract by means of reagents ; and their existence 

 seems to show, on the one hand, that the transparent space 

 through which they extend themselves is only occupied by a 

 watery liquid, and on the other, that the layer of protoplasm 

 which constitutes the primordial utricle, is far from possessing 

 the tenacity of a completely formed membrane. The vibratile 

 filaments pass through the cellulose envelope, which invests them 

 with a sort of sheath ; and in the portion that is within this 

 sheath, no movement is seen. During the active life of the 

 " motile" cells, the vibration of these cilia is so rapid, that it can 

 be recognized only by the currents it produces in the water, 

 through which the cells are rapidly propelled ; but when the mo- 

 tion becomes slacker, the filaments themselves are readily dis- 

 tinguishable; and they maybe made more obvious by the addition 

 of iodine. The multiplication of these motile cells may take 

 place in various modes, giving rise to a great variety of appear- 

 ances. Sometimes they undergo a regular binary subdivision, 

 whereby a pair of motile cells is produced (c), each resembling 

 its single predecessor in possessing the cellulose investment, the 

 transparent beak, and the vibratile filaments, before the solution 

 of the original investment. Sometimes, again, the contents of 

 the primordial cell undergo a segmentation in the first instance 

 into four divisions (D) ; which may either become isolated by the 

 dissolution of their envelope, and may separate from each other 

 in the condition of free primordial utricles (u), developing their 

 cellulose investments at a future time ; or may acquire their cel- 

 lulose investments (as in the preceding case) before the solution 

 of that of the original cell ; and sometimes, even after the disap- 

 pearance of this, and the formation of their own independent in- 

 vestments, they remain attached to each other at their beaked 

 extremities, the primordial utricles being connected with each 

 other by peduncular prolongations, and the whole compound 

 body having the form of a +. This quaternary segmentation 

 appears to be a more frequent mode of multiplication among the 

 "motile" cells, than the subdivision into two; although as we 

 have seen, it is less common in the "still" condition. So, also, 

 a primary segmentation of the entire endochrome of the "mo- 

 tile" cells, into 8, 16, or even 32 parts, may take place (E, F), thus 

 giving rise to as many minute primordial cells. These, when 

 they are set free, and possess active powers of movement, rank 



