PROTOCOCCUS PLUVIALIS. 539 



altogether, (Figs. 27, 28,) so that the entire zoospore 

 appears to consist of only a single, coloured, granular, 

 vesicular disc, corresponding in size with the original 

 enveloping cell. 



The Protococcus plumalis has true motile organs, 

 namely, two long vibratile cilia arising from the pri- 

 mordial cell, and which, passing through two openings 

 in the enveloping cell, move about in the water. These 

 organs, during the life of the cell, move so rapidly that 

 it is then difficult to perceive them ; they are only 

 recognisable by the currents they produce in the water. 

 But when the motion is slackened they are evident 

 enough. They are also rendered very distinct by iodine. 



They are always placed upon the extreme point of the 

 conical elongation, on the anterior end of the primordial 

 cell, and in such a manner as to appear to be immediate 

 continuations of its substance, and as that process itself 

 consists of protoplasm, it is evident that the cilia must 

 be regarded also as composed of the same substance. 

 They appear in some cases to possess an adhesive pro- 

 perty. They resemble, in fact, in all respects, the so- 

 called proboscis of certain Infusoria, such as Euglena and 

 the Monades, and not to differ organologically from the 

 non-vibratile but retractile filaments of Aconita and 

 Actinoplirys. 



It is only that portion of the vibratile filaments beyond 

 the enveloping cell that exhibits any motion, the portion 

 within the outer cell is always motionless, and in that 

 part of their course the filaments appear to be sur- 

 rounded with a sheath. This seems to be the case, 

 not only from the greater thickness at that part, but 

 also from the circumstance, that when, from the pas- 

 sage of the cell into the still condition, the cilia dis- 

 appear, the V-shaped, or forked internal portions remain 

 visible. And it is then, also, that the openings through 

 the enveloping cell become, for the first time, visible 

 (Fig. 46.) Such are the " encysted zoospores" (umhullte 

 Schwarm-zellen.) 



