RECENT MEMOIRS ON FRESHWATER RHIZOPODA. 365 



must have been indeed of almost inconceivable fineness, for 

 in this form the pseudopodia themselves are of extraordinary- 

 tenuity. Greeff does not appear to have detected the true 

 nucleus = my then supposed " vesicula intima/' but, as will be 

 seen, Hertwig and Lesser have detected therein a nucleolus. 

 Those authors constantly found in this species, commingled 

 with the usual fine granules, chlorophyll-granules (or, as they 

 say, "oval chlorophyll-green granules"), never the yellow 

 globules seen by Greeff and myself. I have since myself 

 found this form with only just a few chlorophyll-granules — 

 never the abundant quantity mostly characteristic of A. 

 turfacea ; whilst, on the other hand, the yellow globules, 

 which are most probably of oily nature, certainly of that 

 appearance, are not always present. As Hertwig and Lesser 

 remark, very likely correctly, this fact is most probably 

 to be accounted for by the varying degree of nutrition of the 

 organism. They also describe the not frequently -to-be- 

 observed external contractile vacuoles, which do not, how- 

 ever, cause any projection of the periphery. They have 

 found the nucleus to be somewhat excentric, of a broadly 

 elliptic figure, and, by the application of weak acetic acid, 

 to contain a nucleolus ; under this treatment the latter 

 (not the nucleus itself) assumed a granular appearance 

 (fig. 8, n), the endosarc (fig. 8, k) also assumed a similar 

 but more coarsely granular appearance, the ectosarc (fig. 

 8, r) comparatively unaltered. On applying concentrated 

 acetic acid the latter swelled up, accompanied by a gra- 

 dual solution of the contained colourless granules (perhaps 

 also of the coloured), a change communicated by degrees 

 to the nucleolus, both it and the nucleus now appearing 

 throughout as a homogeneous pellucid vesicle (see fig. 8). 

 In those extremely minute representatives of this form 

 sometimes to be encountered, Hertwig and Lesser have not 

 been able to demonstrate these structures. 



Acanthocystis aculeata, Hertwig et Lesser.^ (Fig. 6.) 



Provided, as characteristic in the genus, with a basal-plate, 

 the spines, like those of A. spinifera, are here subulate and 

 acutely pointed, but they are stouter than in that species, and 

 are more or less curved. The spines are somewhat irregularly 

 posed and pointing various ways, their regular radial arrange- 

 ment being seemingly disturbed by the interposition of minute 

 bacillar pieces lying tangentially, sHghtly curved, correspond- 

 ing to the globular periphery of the body. As to the body- 

 structure — nucleus, endosarc (fig. 6, k), ectosarc {r), which 

 » Loc. cit., p. 201, t. iv, f. 2. 



