Dr. F. Cohn on a neiv genus of the family of Volvocinese. 341 



l)undles of rays passing out from each end; in Volvox, if seen 

 only from above, they give the individual primordial-cells a 

 [Kjlygonal, radiating aspect, and form threads of communication 

 between them : Focke has wrongly considered them as interccl- 

 bilar passages between the individual animalcules. The con- 

 necting threads in Gonium, on the other hand, are something 

 quite different, and do not belong at all to the domain of the 

 protoplasm-filaments, as I shall explain more fully at another 

 opportunity. 



Thus the microscopic analysis, like the chemical investigation 

 of Stephanosphara, in exact analogy with Chlamy do coccus and the 

 swarming-cells of the other Algse, has enabled us to distinguish 

 all the characters of a plant, but not one mark of a true animal 

 organization, in particular not a trace of a mouth, stomach, and 

 sexual organs. But the genus Stephanosphara is thereby pre- 

 eminently important for the decision of the question of the limit 

 between the animal and vegetable kingdom, because the history 

 of its development affords the most convincing proof of the vegetable 

 nature of this genus, and thus of all the other Volvocinese. 



VTI. Development 0/ Stephanosphaera. 



Both the very delicate envelope-cell and the widely distant, 

 transparent green globular primordial-cells of the young Ste- 

 phanosphaera are of a relatively small size. Both grow so much 

 as to double their dimensions during their vegetation ; the former 

 acquires a tough membrane ; the latter fill up the greater part 

 of the envelope-cell, advance towards each other so as to touch, 

 develope thicker, denser contents, and assume most curious 

 forms through the ramification of the protoplasm-filaments, 

 l^'inally the process of propagation shows itself in the primordial- 

 cells. The radiating ends retract all their prolongations, and 

 become rounded into a perfect sphere ; the primordial-cells are 

 now merely attached to the envelope-cell by their cilia, and thus 

 are readily moved from their normal corresponding positions, and 

 then appear devoid of any definite arrangement in the envelope- 

 cell (fig. 8). 



These changes take place in the course of the afternoon; 

 towards evening more infiuential metamorphoses make their ap- 

 pearance. The primordial-cell, namely, extends itself predomi- 

 nantly in one direction in the axis perpendicular to the equatorial 

 ])lane, consequently in the position which fig. 2 represents from 

 above downwards. The two chlorophyll-utricles respectively re- 

 pair to the two ends ; the green contents likewise flow chiefly to 

 the two sides, and leave a broad colourless zone visible in the 

 middle, such as we observe somewhat in the same position in 



