76 DR. G. S WEST ON THE ALGÆ OF 
envelopes. In September many of these small colonies became irregular, and 
in October all of them were irregular and a considerable ‘ange in size Was 
evident. The investments of the larger colonies, which reached a diameter 
of 200 u, were very gelatinous and inconspicuous. Among these larger 
colonies were colonies of an intermediate size, which could be seen clearly 
arising by further cell-division from the small groups with tough envelopes. 
This growth was accompanied by the extension of the inner, more gelatinous 
coats of mucus, as the outer, firmer coats were exfoliated. The second, 
A-—F, Stages in the life-history of Spherveystis Schroeteri as seen in the 
H А 2 Yy 
plankton of the Yan Yean Reservoir, x300. 
A and B, typical Spherocystis-stage; C, group of daughter-cells escaped from 
3 Л / c~? ^ c I o 
larger colony ; D, growth of colony C by exfoliation of tougher outer mem- 
branes; E, further advanced ; Е, Tetraspora-stage. 
irregular type of colony was abundant from October to December, reaching 
its maximum abundance in November, and it appears to me that it must be 
regarded as identical with the Alga described by Lemmermann as Tetraspora 
lacustris. 
The different colonies described above are stages in the life-history of one 
Alga, the Splurrocystis-type of colony flourishing from February to August, 
and then giving rise to the imperfect Tetraspora-ty pe, which is abundant from 
September to December. No trace of the Alga was observed in the January 
collections. 
