310 DR. Е. E. FRITSCH ON FRESHWATER ALG.E 
pyrenoid was often visible, and a considerable amount of the characteristic 
fat was mostly present *. Хо reproductive or resting-stages were observed. 
It seems to me that the reference of this species to the genus Pteromonas 
is in no way certain f. The genus includes a number of species, which are 
actively motile forms provided with two cilia. In the case of P. nivalis, 
however, no cilia have been recorded, nor was I able to make out any traces 
of them in the yellow snow specimens. Onthis point Chodat (* Algues vertes, 
р. 146) remarks: * cellules parfois mobiles, ordinairement immobiles ; cils 
inconnus." Ме Ё, їп his later description of this species, does not refer to 
any movement, in fact he regards the winged cells as resting-stages (aplano- 
spores), and looks upon certain cells (“ spindelfórmige, an dem einen Ende 
etwas abgestumpfte Zellen," p. 168), which he figures on pl. 3. fig. 46 
(ef. Chodat’s fig. 70 Е), as zoospores of the Pteromonas which had come to 
rest; possibly my fig. 31 may correspond to these cells. In view of the fact, 
however, that neither Chodat nor Wille nor I have seen any trace of cilia on 
either type of cell, these interpretations appear somewhat forced. À much 
simpler view would be to regard the typical winged form (as shown in 
Chodat's figs. 70 A, В, C, and my figs. 22-24) as the normal motionless 
individual and the unwinged cells (Chodat’s fig. 70 К, Wille's fig. 46, and my 
fig. 31) as young individuals, possibly formed hy division of the contents of 
a mother-individual, and in which wings have yet to arise (cf. Chodat’s 
fig. 70 №) ; the correctness of this view depends mainly on the nature of the 
movement observed by Chodat. If my interpretation of Pteromonas nivalis 
is correct, it is obviously out of place in the genus Pteromonas and must be 
referred to Scotiellu as S. nivalis (Chod.), Е. E. Fritsch. With the genus 
Scotiella it agrees in several respects, viz.: the single chloroplast with a 
pyrenoid ; the wings (cf. especially the optieal section shown in Chodat's 
Но. 70J with my optical section of Scotiella antarctica, fig. 11) ; the behaviour 
of these wings at the two ends of the cell (* qui se prolongent vers les 
extrémités en arête saillante,” according to Chodat, p. 146 ; “ An beiden Enden 
des Zellinhalts finden sich Vorsprünge . . . . sicherlich nur dadurch entstanden, 
dass die Rippen der Membran etwas vorsprangen," according to Wille, 
pp. 169, 170 ; cf. also my fig. 23) ; and, lastly, the apparent formation of new 
individuals by subdivision of the cell-contents $. 
ж Chodat describes the cells of Pteromonas nivalis as “ ordinairement remplie d'une huile 
jaune-dorée” (p.146), which may well correspond to the yellow fat observed in the individuals 
of the yellow snow. Wille (4^ Algologische Notizen, XL-XIV.," in Nyt Magazin f. Natur- 
videnskab. xli. 1903, p. 170), however, speaks of the contents of the cells being generally 
coloured almost quite red by hematochrome. This is interesting, as indicating that one and 
the same snow-form may exhibit different pigments in different localities. 
+ Cf. Wille, Гос. cit. p. 171. { Loc. cit. 
$ Wille (Joc. cit. p. 171) also suggests on the basis of his observations that it may become 
necessary to remove Pteromonas nivalis from the genus Pferomonas ; this is based on his 
view that the ordinary winged cells are aplanospores (resting-cells), that reproduction is 
