FRESHWATER ALO* OF THE SOUTH ORKNEYS. 121 



Orkneys that \\.-rv obviously preserved in nn active, motile condition. Tin- promim-m 

 features of this species, as describe<l by Wille, are the protrusion of the posterior end of 

 the individual into a conical tij> (figs. 37, 38), which is often somewhat bent to one 

 (flu- INI), tin- fact thai tin- two cilia are about |al in length to the body of the cell, 

 and that the strongly tlm k- n-d base of the chloroplast contains a median rounded 

 l>\r. noid (figs. 37, 38). There can be no doubt that the individuals observed belong 

 to thia species, although one or two minor points of difference were noted. The cilia 

 were frequently found to be as much as one and a third times the length of the cell 

 (not shown in the figures) ; they were nearly always curved back or spread out at right 

 angles to the body of the cell (figs. 37, 38), as Wille shows them. The size of the 

 ordinary individuals varies considerably ; length - 13-20 M, breadth = 7-10 M, but some 

 of the dividing individuals are much larger. The pointed posterior end, as a general 

 rule, lies in the same straight line as the axis of the individual, but bending was not 

 uncommon. The cell-membrane is almost invariably much more prominently thickened 

 at the pointed posterior end, and not uncommonly individuals are found in which the 

 whole of the pointed portion consists of solid membrane (fig. 39). In many cases 

 (cf. Wille, loc. cit.) the posterior part of the protoplasmic contents is also pointed 

 and in the living individual probably in direct contact with the pointed cell-wall, 

 alt hough in preserved material generally separated from it by a space (cf. how- 

 ever fig. 38). But in a considerable number of individuals, the back end of the 

 protoplasmic body was rounded off and separated by a marked interval from the 

 pointed tip ; it seems that this may be a preliminary to cell-division, as all dividing 

 individuals were found to have the protoplast rounded off in this way (cf. fig. 35). 

 Many examples of division (from the presence of two pyrenoids in the cell up to 

 the formation of two daughter-individuals, fig. 35) were observed ; in all cases such 

 divisions were longitudinal and took place after withdrawal of the cilia. Curious 

 division-stages were found in the form of very large individuals (in this case with 

 or without cilia) containing a considerable number (eight or more) of protoplasmic 

 units, each with a pyrenoid (fig. 36) ; such individuals may possibly have been 

 forming gametes. The prominent beak at the point of origin of the cilia, described 

 and figured by Wille, was often difficult to recognise. On the other hand, in a few 

 cases there was a very pronounced development of this beak (fig. 40) in the form 

 of a rounded protrusion, from the base of which the cilia arose. Apart from these 

 peculiarities, the Antarctic form showed all the features described by Wille, viz. 

 ribbing of the basin-shaped chloroplast, an elongated stigma (rarely visible), con- 

 tractile vacuoles, etc. 



2. CHLAMYDOMONAS KIIHKNBKKGII, Gorosch., Bull. Soc. imp. d. Nat. de Moteou, 

 1890, No. 3, p. 128-131, pi. iii., figs. 10-25. 

 Samples 10 and 11, common. 



Probable zygospores observed in sample 1 1. 



VOL. ill. ie 



