Prof. Meyen on Red and Green Snow. 247 



})ear in almost incredible numbers, and, surrounded with a 

 kind of slime, form more or less thick skins, which often 

 cover tlie bottoms of shallow standing waters, particularly of 

 ditches, etc. Such green skins will sometimes remain several 

 mouths, not only in the natural state, but also in a room, and 

 only occasionally do some of the green globules pass into the 

 active state ; they stretch themselves, exhibit the rostrum, etc. 

 In comparison to the immense mass of young and old indivi- 

 duals, very few only pass out of this to all appearance vegetable 

 mass into free moving animalcules. M. Agardh, in 1823, 

 saw in red snow that the globules generally considered as ve- 

 getables sometimes pass into animalcules ; and the behaviour 

 of the EncheUdes in the passive and active state is the reason 

 why so many philosophers have spoken of a metamorphosis of 

 Infusoria into plants. One would be obhged in fact to hold 

 these spherical, inactive EncheUdes as plants if solitary ones 

 did not occasionally begin to move, and if one had not ob- 

 served their origin. When the animalcules contract them- 

 selves, the rostrum is laid along the side, but only in the first 

 stages is it observable. However, there still remains some- 

 thing mysterious in this passive state of the EncheUdes and in 

 their rare increase : by repeated observations it may j)erhaps 

 be explained. It is still a question whether EncheUs Pulvis- 

 cuhis and En. sanguinea, which colour the snow now green, 

 now red, are really one and the same animalcule. M. 

 Ehrenberg has, it is true, characterized each, both by de- 

 scriptions and by delineation, as different species : in the red 

 ones he saw several grain-like balls in the interior ; but from 

 the drawing it is evident that these are the same as the young 

 globules observed by myself in the green animalcules. M. 

 Ehrenberg erroneously regards them as coloured eggs, which 

 are first green, then become red and are enclosed in the 

 gastric cells. He saw that the red animalcules were larger 

 than the green ones ; but M. Martins observed that the red 

 bladders in snow vai'ied much in size ; and I myself have often 

 found individuals of Ench. Pulviscidus, which were consider- 

 ably larger than the usual red animalcules, and quite as large 

 as they occasionally are, on which account the size cannot be 

 taken as a distinguishing character. 



M. Ehrenberg relates of the red EncheUdes that several 

 are still quite green, while others appear spotted, half red and 

 half green ; and this might perhaps be taken as the best proof 

 that these so differently coloured Infusoria belong to one and 

 the same species. I myself could never distinguish a red from 

 a green one when individuals of equal size were compared 

 together. It is true we have as yet no explanation, how red 

 can be changed into green, or vice versa; but we know that 



