478 Annals of the South African Museum. 



the same species. The second conspicuous form, which eventually 

 becomes dominant, consists of irregularly rounded, lobed or elongated, 

 sometimes branched masses composed of large numbers of rounded 

 cells in a gelatinous matrix, very similar to a Tetraspora, but showing 

 no signs of pseudocilia. As there has in the past been considerable 

 difference of opinion as to whether similar masses found associated 

 with Sphaerocystis Schroeteri were actually a phase in the life of that 

 alga or a species of Tetraspora (West, W. & G. S., 1912, p. 413) it 

 was particularly interesting to find the two forms here, linked up by 

 every stage in transition from one to the other. 



Finally, a third striking form, comparatively rare and only seen 

 during fairly early stages of development of the pool, consists of 

 botryoidal clusters of rounded aggregates of groups of very small 

 cells, similar to very young spheres of the first stage. These have no 

 firm exterior lamella to the gelatinous envelope, the presence of 

 which cannot be detected until after treatment with some stain, 

 e.g. iodine or methylene blue. When first seen such colonies suggested 

 a Dictyosphaerium or Westella in general form, but no signs of con- 

 necting strands could be distinguished. It is apparently inter- 

 mediate between the spherical form and the Tetraspora-like phase ; 

 the gelatinous envelope of a sphere in which the cells of the groups 

 have already divided loses its firm outline, and the daughter spheres, 

 instead of escaping separately, remain in contact with one another, 

 without developing outer membranes. Continued division soon 

 results in an amorphous gelatinous mass containing numberless cells 

 such as is characteristic of the palmelloid Te^ras^ora-phase. 



Obviously a study of living material of this very interesting and 

 somewhat puzzling alga is highly desirable. 



Mixed with the various forms of Sphaerocystis is yet one more 

 arresting alga, a very large species of Kirchneriella Schmidle. It is 

 characterised by the large size of the colonies, often over 2 mm., 

 sometimes as much as 4 mm. long, and the great number of cells 

 composing them. It is usually much less abundant than the Tetra- 

 spora-iorm. of Sphaerocystis which it much resembles in general form 

 and appearance ; but in fairly early stages of the pool's development 

 (e.g. 8th February, see Table I) it may far outnumber the latter, 

 and is then usually associated with comparatively numerous colonies 

 of the botryoidal form of that alga. 



These gelatinous colonial algae can evidently thrive in quite 

 shallow water in which the temperature at midday must be high, 

 continuing to do so for some days after conditions have become 



