248 DEVELOPMENT OF PROTOCOCCUS : — MOTILE FORM. 



produced assume the ' motile ' condition ; being liberated before 

 the development of the cellulose envelope, and becoming furnished 

 with two long vibratile filaments, or cilia, which appear to be 

 extensions of the primordial utricle (h). In this condition it 

 seems obvious that the colourless protoplasm is more developed 

 relatively to the colouring-matter, than it is in the ' still ' cells ; 

 it generally accumulates in the part from which the vibratile fila- 

 ments or cilia proceed, so as to form a sort of transparent beak 

 (h, k, l) ; and it usually contains 'vacuoles,' occupied only by 

 clear aqueous fluid, which are sometimes so numerous as to take 

 in a large part of the cavity of the cell, so that the coloured con- 

 tents 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 is not so firm in its consistence (i, k, l). 

 Thread-like extensions of the protoplasm, sometimes containing 

 coloured globules, are not unfrequently seen to radiate from the 

 primordial utricle towards the exterior of this enveloping bag (i) ; 

 these are rendered more distinct by iodine, and can be made to 

 retract by means of re-agents ; 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 primor- 

 dial utricle is far from possessing the tenacity of a completely 

 formed membrane. — The vibratile cilia pass through the cellulose 

 envelope, which invests their base 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 quickly pro- 

 pelled ; but when the motion becomes slacker, the filaments them- 

 selves are readily distinguishable ; and they may be made more 

 obvious by the addition of iodine. 



190. The Multiplication of these 'motile' cells may take place 

 in various modes, giving rise to a great variety of appearances. 

 Sometimes they undergo a regular binary subdivision, whereby a 

 pair of motile cells is produced (c), each resembling its single pre- 

 decessor in possessing the cellulose investment, the transparent 

 beak, and the vibratile filaments, before the solution of the ori- 

 ginal investment. Sometimes, again, the contents of the primor- 

 dial 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 con- 

 dition of free primordial utricles (h), developing their cellulose 

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

 vestments (as in the preceding case) before the solution of that of 

 the original cell ; and sometimes, even after the disappearance of 

 this, and the formation of their own independent investments, 



