410 Dr. F. Cohn on a new genus of the family o/* Volvocinese. 



Fig. 5. Equatorial view as in fig. 4 ; the primordial-ceils are more crowded 



into one hemisphere of the envelope-cell. 

 Fig. 6. Polar view ; only six primordial-cells exists but the upper two are 



twice as large as the others. 

 Fig. 7. Polar view ; the envelope-cell contains only four primordial-cells, 

 the product of the second division having become a " permanent 

 generation." 

 Fig. 8. Commencement of the formation of macrogonidia ; the primordial- 

 cell * is still unaltered ; the cell ** exhibits a flow of the contents 

 towards the two ends ; the primordial-cell in the middle has di- 

 vided into two, the rest already into four secondary cells. 

 Fig. 9. All the eight primordial-cells have divided, in the four secondary 



cells of the second " transitional generation." 

 Fig. 10. The division already advanced to the third " permanent genera- 

 tion," so that each primordial-cell has separated in eight wedge- 

 shaped pieces. 

 Fig. 1 1 . The young StephanosphcBrce produced by the division have become 

 more organized, the colourless connected mass of protoplasm in 

 the middle having been gradually constricted and cut off; they 

 already begin to move inside their envelope : at a, two are seen in 

 the side view. 

 Fig. 12. The division completed and the eight young StephanosphcBrce ro- 

 tating in the common envelope. 

 Fig. 13. A young Stephanosphcera just emerged ; its cilia are only visible 



by the eddy they produce in the water. 

 Fig. 14. A similar one killed by iodine, in the polar view; it exhibits the 

 cilia and the common envelope-cell which is closely applied to 

 the periphery of the primordial-cells. 

 Fig. 15. A somewhat older Stephanosphcera ; the envelope-cell still has the 

 form of a flat, tabular spheroid, and therefore appears as an ellipse 

 in the equatorial view. 

 Fig. 16. Commencement of the formation of microgonidia ; the eight pri- 

 mordial-cells dividing in a higher power of two. 

 Fig. 17- The eight original primordial-cells have been broken up into their 



microgonidia, which swarm about in the common envelope. 

 Fig. 18. The same stage as in fig. 17; one primordial-cell, a, has taken on 

 the formation of macrogonidia and become developed into a 

 young Stephanosphara, which rolls along among the crowd of 

 microgonidia. 

 Fig. 19. A few microgonidia after their exit from the envelope-cell : a, mo- 

 ving actively in water ; the rest killed with iodine and exhibiting 

 four cilia. 

 Fig. 20. A primordial-cell, which after secreting a special coat in a Chla- 

 mydomonas-like condition, has emerged from the common en- 

 velope-cell to pass subsequently into a state of rest. 

 Fig. 21 . Diagram to illustrate the laws of division in the macrogonidia of 

 StephanospkeBra ; first the septum a, m, b, n, is formed, then the 

 second through c, m, d, n, — these two generations are " transi- 

 tional ;" the eight cells produced by the septa h, m, g, n and e, m, 

 f, n, become a " permanent " generation. 



The figures are represented magnified 300 times, except fig. 19, which 

 is 500 times. 



