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



duces a ' very irregular course ; in this way these organisms 

 screw themselves^ as it were, onwards in the water. Sometimes 

 they swim straight out with uniform rapidity, the pole going 

 first, the rotating ring of primordial- cells standing at right 

 angles to the course and appearing only in one line ; sometimes 

 they turn round, so that the equatorial plane presents itself as a 

 circle again (in the polar view) : they rotate thus round their 

 centre without moving from the spot ; then they set one pole 

 forward and swim on in another direction, bend to the right or 

 to the left, or turn quite round, mostly without any perceptible 

 obstruction, move in curves of the most varied kinds, run round 

 any point in spii'al lines, come into different planes, sometimes 

 ascending, sometimes descending ; in short, they exhibit all those 

 most complex and wonderful phsenomena of locomotion, which 

 we are acquainted with in the moving propagative cells of the 

 Algse, and, as I have demonstrated elsewhere*, in exactly the 

 same way in the Astomous and Anenterous Infusoria {Monadina, 

 Astasicea, Crypt omonadina, &c.), and which certainly do not bear 

 at all the character of purposing, conscious volition, but appear 

 as an activity determined not indeed by purely external causes, 

 but by internal causes in the organization and vital process. The 

 collective idea of such motions is best represented by the course 

 described by a top which runs through the most varied curves 

 while at the same time constantly revolving on its axis. 



I have endeavoured in vain to determine whether the ro- 

 tation round the axis, in the organism here described, is con- 

 stant in one given direction. To render such a determination 

 possible, it would first of all be requisite that the rotating globes 

 should allow the recognition of a right or left, or what is the 

 same, a top and bottom, and the marking of these by morpho- 

 logical differences. Such a determination, however, is altogether 

 impossible in very many cases, in our organisms, since the en- 

 velope-cell, as we have seen, is a perfect globe, while the pri- 

 mordial-cells are mostly symmetrically developed toward each 

 end in the longer axis. Under such circumstances there exist 

 no characters for the distinction of the two poles of the envelope- 

 cell, to regard one as the upper, the other as the lower ; and in 

 the same cases to demonstrate a revolution in one fixed direction 

 is altogether out of the question. 



We might certainly distinguish the two poles by calling that 

 the upper which goes first in the motion. In many cases such a 

 diflPerence is already given in the organization, where, namely, 

 the piimordial-cells are un symmetrically developed, projecting 



* Nachtrage zur Naturgeschichte des Protococcus (Chlamydococcus) 

 pluvialis (Nova Acta Ac. C. C. L. n. c. xxii. pars 2. p. 73.5). 



