DEVELOPMENT OF PEOTOCOCCUS. 249 



they remain attached to each other at their beaked extremities, 

 the primordial utricles being connected with each other by pedun- 

 cular 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 'motile' cells, into 8, 16, or even 

 32 parts, may take place (e, f), thus giving rise to as many minute 

 primordial cells. These Micro-gonidia, when set free, and possess- 

 ing active powers of movement, rank as Zoospores (g) : they may 

 either develope 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 vibratile cilia, 

 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 cilia. 



191. 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 as Ghlamydomonas, Eughna, Trachelomonas, Gyges, 

 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 

 exclusively and then principally ; they gradually diminish, become 

 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 extra- 

 ordinary amount ; and this alternation 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 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 proceed to the forma- 



* 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, but which differs from that in which they will be foimd in the 

 original Memoir ; and he is glad to be able to state, from personal com- 

 mimication with its able Author, 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. 



