Dr. P. Cohn on a new genus of the family o/" Volvocinese. 343 



already completely separated into eight, while one or other of 

 them is still wholly unaltered. 



When the act of division has gone on favourably up to the 

 point to which we have followed it above, some hours elapse be- 

 fore the young families of cells escape completely from the enve- 

 lope. The process which precedes their birth consists principally 

 in the more complete isolation, in a centrifugal direction around 

 their common centre, of the secondary-cells produced by each 

 primordial-cell. Since the parting off of the secondary-cells ad- 

 vances gradually from the periphery towards the centre, they are 

 already completely individualized and separated by intercellular 

 spaces at the periphery, while all eight remain still connected in 

 the centre into a common colourless mucous mass filled with 

 protoplasm-granules (fig. 11). But the flow of the contents 

 from the centre to the borders, which continues up to this time^ 

 at length causes the constriction of the central mass of protoplasm 

 also into eight parts ; the eight secondary-cells then appear of a 

 deep yellowish green externally, passing internally into colourless 

 green towards finely granular beak^ which are all connected in 

 the centre, but become gradually attenuated, torn away and re- 

 tracted (figs. 10, 11, 13, 14). Then the young primordial-cells 

 become rounded into short cylinders and stand in a circle, with- 

 out organic connexion, but placed closely beside one another : 

 seen from above (in the polar view), under the microscope, they 

 resemble a wheel with eight notches ; from the side, examined 

 in the equatorial view, we see four or eight short cylinders lying 

 side by side, so that the whole is not unlike a small Scenedesmus 

 obtusus (fig. W a). 



The primordial-cell undergoing division behaves as a whole 

 towards external things, until the parting off into eight is quite 

 completed ; that is to say, its two cilia move uninterruptedly, 

 and consequently the entire Stephanosphara-glohe still rolls 

 through the water according to the known laws, even when most 

 of its primordial-cells have already become more or less com- 

 pletely divided into four or eight secondary-cells. Only shortly 

 before the completion of the division do the cilia of the parent- 

 cell lose their motion and disappear, it may be by being retracted 

 or by being thrown off; but the orifices through which the cilia 

 previously passed out into the water, may now be observed in the 

 common envelope-cell, as minute points surrounded by a thick- 

 ened border. 



Immediately after that, it is seen that the newly-formed 

 secondary-cells have developed their own cilia; for the young 

 generations formed in the interior of the parent-envelope now 

 begin to move and to roll over like a wheel, so far as the con- 

 fined space allows of this (figs. 11, 12). Inconsequence of this 



