Dr. F. Cohn on a new genus of the family of Volvocinese. 327 



ihe transformations which the primordial-cells pass through in 

 consequence of external influences. Under certain circumstances, 

 namely, the filiform processes may be retracted, being torn away 

 from the envelope-cell and taken up into the substance of the 

 primordial-cells ; the produced ends of the primordial-cells also 

 disappear, the latter becoming rounded off into their original 

 spherical or short cylindrical form. Such a change would be 

 impossible if the primordial-cells were surrounded by a rigid 

 membrane, such as that of the envelope-cell for example. Still 

 more rapid and decided are the metamorphoses which the pri- 

 mordial-cells undergo in the interior of the envelope-cell, through 

 influences destructive to the life of the organism. These phae- 

 nomena, usually called dissolution, do not change the rigid en- 

 velope-cell at all; but they totally decompose the primordial- 

 cells, depriving them of their form and dissolving them into a 

 single structureless green mass, which lies upon the inside of 

 the envelope-cell, frequently destroying all evidence of the origin 

 from eight spheres, while not a trace of special enveloping mem- 

 branes comes to light. These phsenomena of dissolution more- 

 over indicate that the envelope-cell, as I have already mentioned, 

 is composed of a delicate membrane enclosing a clear watery fluid, 

 which cannot be dense, gelatinous or mucilaginous, since it is 

 readily displaced by the radiating filaments and the dissolved 

 substance, and which therefore is very similar to pure water, if 

 not exactly the same. 



II. Motion. 



The cilia which are protruded from the equator of the en- 

 velope-cell are but short inside this, but the portion projecting 

 into the water is much longer and vibrates actively, thereby causing 

 all the movements. During their vibration the cilia are difficult 

 to detect ; but when di'ied on glass, and still better by wetting 

 them with iodine, they may readily be traced in their whole 

 length, especially if sulphuric acid is added, this rendering them 

 more distinct and giving them a darker colour. The motion of 

 the entire organism, depending on the eight pairs of cilia, exactly 

 resembles that well known in the Algce and many Infusoria. First 

 there is a rapid revolution round that axis of the envelope-cell 

 which passes through its poles and stands perpendicular to the 

 ring of primordial-cells, so that the envelope-cell rotates like a 

 wheel upon its axle. In the polar view (figs. 1, 3) our form 

 gives exactly the impression of a revolving wheel, while in the 

 equatorial view (figs. 2, 4), where the primordial-cells are mostly 

 elongated, it has more the aspect of a globe turning upon its 

 axis. Besides this revolution on its axis, which endures through- 

 out the whole life, there is an advancing movement, which pro- 



