VARIOUS CONDITIONS OF PROTOCOCCUS. 257 



as "zoospores" (&): which may either develope a loose cellulose 

 investment or cyst, so as to attain the full dimensions of the or- 

 dinary motile cells (i, k), or may become clothed with a dense 

 envelope, and lose their vibratile cilia, thus passing into the 

 "still" condition (a) ; and this last transformation 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 cilia. 



155. All these varieties, whose relation to each other has been 

 clearly proved by watching the successional changes that make 

 up the history of this one Plant, have been regarded as consti- 

 tuting, not merely distinct species, but distinct genera of Animal- 

 cules; such us, CMamydomonas, Iluglena,''Trachelomonas, Qyges, 

 Q-onium, Pandorina, Botryocystis, Uvella, Syncrypta, Monas, As- 

 tasia, Bodo, and probably many others.^ Certain forms, such as 

 the "motile" cells (i, K, l), appear in a given infusion, at first 

 exclusively and then principally ; they gradually diminish, be- 

 come more and more rare, and finally disappear altogether, being 

 replaced by the " still" form. After some time, the number of 

 the "motile" cells again increases, and reaches, as before, an ex- 

 traordinary amount ; and this alteration may be repeated several 

 times in the course of a few weeks. The process of segmentation 

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

 cells be transferred from a larger glass into a small capsule, 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 fol- 

 lowing 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 in the "motile." 



' In the above sketch, the Author has presented the facts described by Dr. Cohn, 

 under the relation which they seemed to him naturally to bear; for the membrane 

 which immediately surrounds the primordial utricle of the " still" cells, appears to him 

 to be essentially the same with the sacculated investment of the "motile" form, since it 

 differs only in its greater density, and in the absence of the interposed liuid. It is dis- 

 tinctly stated by Cohn, towards the conclusion of his Memoir, that the one like the other 

 consists of cellulose, since both alike give the characteristic blue color with a very dilute 

 solution of iodine, and with moderately diluted sulphuric acid ; yet he speaks of what 

 he terms the " encysted zoospore'' (i, K, l), as being formed by one cell vnthin another, 

 the outer cell having a true cell-membrane and aqueous contents, but being destitute of 

 primordial utricle; whilst the inner cell has denser, colored contents, but is without the 

 true cell-membrane. Having enjoyed, since the above was written, the opportunity of 

 personally communicating with Dr. Cohn witii regard to the question to which it refers, 

 the Author is glad to be able to state, that Dr. Cohn's later observations have led him to 

 adopt a' view of the relationship of the " still'' and " motile" forms, which is in essential 

 accordance with his own. 



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