MICROSCOPIC FORMS OF VEGETABLE LIFE. 235 



lomonas, G-yges, Gonium, Pandorina, Botryocystis, Uvella, Syncrypta, 

 Monas, Astasia, Bodo, and probably many others. Certain forms, such 

 as the ' motile ' cells I, K, L, appear in a given infusion, at first exclu- 

 sively and then principally; they gradually diminish, become more and 

 more rare, and finally disappear altogether, being replaced by ' still' form. 

 After some time, the number of the ( motile ' cells again increases, and 

 reaches, as before, an extraordinary amount; and this alternation may be 

 repeated several times in the course of a few weeks. The process of seg- 

 mentation is often accomplished with great rapidity. If a number of 

 motile cells be transferred from a larger glass into a smaller, it will be 

 found, after the lapse of a few hours, that most of them have subsided to 

 the bottom; in the course of the day, they will all be observed to be upon 

 the point of subdivision; on the following morning, the divisional brood 

 will have become quite free; and on the next, the bottom of the vessel will 

 be found covered with a new brood of self -dividing cells, which again pro- 

 ceed to the formation of a new brood, and so on. The activity of Motion 

 and the activity of Multiplication seem to stand, in some degree, in a 

 relation of reciprocity to each other; for the self-dividing process takes 

 place with greater rapidity in the 'still' cells, than it does in the 'mo- 

 tile.' 



234. What are the precise conditions which determine the transition 

 between the ' still ' and the ' motile ' states, cannot yet be precisely stated; 

 but the influence of certain agencies can be predicted with tolerable 

 certainty. Thus it is only necessary to pour the water containing these 

 organisms from a smaller and deeper into a larger and shallower vessel, 

 at once to determine segmentation in numerous cells a phenomenon 

 which is observable also in many other Protophytes. The ' motile ' cells 

 seem to be favorably affected by Light, for they collect themselves at 

 the surface of the water and at the edges of the vessel ; but when they are 

 about to undergo segmentation, or to pass into the 'still' condition, they 

 sink to the bottom of the vessel, or retreat to that part of it in which they 

 are least subjected to light. When kept in the dark, the 'motile' cells 

 undergo a great diminution of their chlorophyll, which becomes very pale, 

 and is diffused, instead of forming definite granules; they continue their 

 movement, however, uninterruptedly, without either sinking to the bot- 

 tom, or passing into the still form, or undergoing segmentation. A mod- 

 erate warmth, particularly that of the vernal sun, is favorable to the 

 development of the 'motile' cells; but a temperature of excessive eleva- 

 tion prevents it. Rapid evaporation of the water in which the ' motile > 

 forms may be contained, kills them at once; but a more gradual loss, 

 such as takes place in deep glasses, causes them merely to pass into the 

 'still 'form; and in this condition especially when they have assumed 

 a red hue they may be completely dried-up, and may remain in a state 

 of dormant vitality for many years. It is in this state that they are 

 wafted-about in atmospheric currents, and that, being brought-down by 

 rain into pools, cisterns, etc., they may present themselves where none 

 had been previously known to exist; and there, under favorable circum- 

 stances, they may undergo a very rapid multiplication, and may maintain 

 themselves until the water is dried-up, or some other change occurs which 

 is incompatible with the continuance of their vital activity. They then 

 very commonly become red throughout, the red coloring-substance ex- 

 tending itself from the centre towards the circumference, and assuming 

 an appearance like that of oil-drops; and these red cells, acquiring thick 

 cell-walls and a mucous envelope, float in flocculent aggregations on the 



