338 Br. F. Cohn on a new genus of the family 0/ Volvocineae. 



VI. Comparison of Stephanosphsera with Chlamydococcus. 



If we now compare the conditions of organization of Stepha- 

 nosphcera with those of Chlamydococcus which we have just in- 

 dicated, we find the most essential agreement. In the first place 

 the envelope-cell of Stephanosphcera corresponds exactly to that 

 of the moving macrogonidia of Chlamydococcus ; it is composed 

 of a delicate colourless membrane and contents resembling water. 

 Chemical actions to which I subjected the envelope-cell of Ste- 

 phanosphcsraj bear witness of this agreement in the most minute 

 particulars. The envelope-cell is indifi*erent to acids and alkalies 

 and is not dissolved in them ; but it suffers a peculiar thickening 

 by sulphuric acid which causes it to apply itself more closely to 

 the primordial-cell_, and present itself very distinctly and clearly 

 defined. In general the application of dilute sulphuric acid is 

 often the best means of making clear delicate vegetable mem- 

 branes which would otherwise be readily overlooked, especially 

 when iodine is added, which then ordinarily colours the mem- 

 brane yellow. The cilia also are rendered more distinct by sul- 

 phuric acid. The envelope-cells of Pandorina, Chlamydococcus 

 and Volvox behave in exactly the same way. 



With regard to the chemical composition of the envelope-cell 

 of Stephanosphcera, I have succeeded in demonstrating in it also 

 the most decisive criterion of a vegetable membrane. Since 

 Nageli, in his comparison of the Unicellular Algae with the simple 

 animal cells, arrived at' the result, that all distinctions hitherto 

 proposed between the lowest forms of the two kingdoms are 

 fallacious, and that the only decisive criterion must lie in the 

 nature of the membrane, which belonged in animals to the 

 proteine series, and in plants to the group of hydrates of carbon 

 ■ — since that epoch attention has necessarily been directed, in all 

 amphibolic structures, to the investigation of the chemical com- 

 position of their membrane. I have succeeded in demonstrating 

 the characteristic reaction of vegetable cellulose, the blue colouring 

 hy iodine and sulphuric acid, in the envelope-cell of Stephano- 

 sphaera. For this purpose it is requisite to allow a drop qI pretty 

 concentrated sulphuric acid to act upon the swarming Stephano- 

 5pto'«-globes until the green primordial-cells in the interior are 

 decomposed, by which time the proper transformation of the 

 envelope-membrane has taken place, and a drop of solution of 

 iodine (iodine in iodide of potassium), sufficiently diluted to pre- 

 vent the sulphuric acid precipitating it in crystals, then produces 

 a coloration of the envelope, which appears at first violet, gradually 

 becoming more intense, and at last beautiful indigo blue. Thus 

 the chemical behaviour of the envelope-cell in Stephanosphara, as 



