234: THE MICROSCOPE AND ITS REVELATIONS. 



tion it seems obvious that the colorless protoplasm is more developed 

 relatively to the coloring matter, than it is in the ' still ' cells; 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 colored contents seem only like a deposit on its walls. 

 Before long, this ' motile 7 cell acquires a peculiar saccular investment, 

 which seems to correspond with the cellulose envelope of the ' still' cells, 

 but is not so firm in its consistence (i, K, L); and between this and the 

 surface of the ectoplasm a considerable space intervenes, traversed by 

 thread-like extensions of the latter, which are rendered more distinct by 

 iodine, and can be made to retract by means of re-agents. The flagella 

 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 f motile ' cell, the vibration of these 

 flagella is so rapid, that it can be recognized only by the currents it pro- 

 duces in the water through which the cells are quickly propelled; but 

 when the motion becomes slacker, the filaments themselves are readily 

 distinguishable; and they may be made more obvious by the addition of 

 iodine. 



232. 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 (B), 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 dissolution 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 dissolu- 

 tion of their envelope, and may separate from each other in the condi- 

 tion of free primordial utricles (H), developing their cellulose investments 

 at a future time; or may acquire their cellulose investments (as in the 

 preceding case) before the solution of that of the original cell; while some- 

 times, even after the disappearance of this, and the formation of their 

 own independent investments, 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 sub- 

 division into two; although, as we have seen, it is less common in the 

 ' still ' condition. So, also, a primary segmentation of the entire endo- 

 chrome of the 'motile' cells into 8, 16, or even 32 parts, may take place 

 (E, F), thus giving rise to as many minute gonidial cells. These micro- 

 gonidia, when set free, and possessing active powers of movement, rank 

 as ' zoospores ' (G) : they may either develop a loose cellulose investment 

 or cyst, so as to attain the full dimensions of the ordinary motile cells 

 (i, K), or they may become clothed with a dense envelope and lose their 

 flagella, thus passing into the ' still ' condition (A) ; and this last trans- 

 formation may even take place before they are set free from the envelope 

 within which they were produced, so that they constitute a mulberry- 

 like mass, which fills the whole cavity of the original cell, and is kept in 

 motion by its flagella. 



233. These varied forms, whose relation to each other has been clearly 

 proved by watching the successional changes that make up the history of 

 this one riant, have been described, not merely as distinct species, but as 

 distinct genera of Animalcules, such as Chlamydomonas, EuglcnaTrache- 



