1 45 
The British Freshwater Algce. 
organisms.” Now there is not the slightest justification for this 
strong language. Scarcely a single one of the facts or considerations 
that Mr. West has adduced in support of his contention that the 
Desmids are descended from filamentous forms, but could be used 
to support the view that the filamentous forms are descended from 
Desmids, or, at any rate, unicellular common ancestors of the two 
groups. It is the old story of a series which can be read either 
way. It is just as easy to suppose that the primitive Conjugates 
were simple unicellular forms (nearest the Saccodermae) with iso- 
gamous conjugation, and that these gave rise on the one hand to 
filamentous types with incipient sexual differentiation, and on the 
other to unicellular types with complicated external forms and very 
occasional sexual differentiation, as to suppose that sex was 
gradually lost in the evolution of Desmids from Zygnemaceae. The 
occasional “reversion” to sex in Hyalotlieca may just as well be a 
progressive modification. The absence of zoospores (p. 148, 
footnote) is no evidence, because the hypothetical filamentous an¬ 
cestors of the Zygnemaceae are every bit as likely to have possessed 
zoospores as the unicellular ancestors of the Desmids on the 
other hypothesis, judging by the actual distribution of motile cells 
in the existing filamentous and unicellular algae respectively. The 
only piece of evidence brought forward by Mr. West that seems at 
all cogent is the great resemblance between Microspora Ldfgrenii 
and Zyguema pachydermum, and this may of course be accidental. 
The most likely view of the phylogeny of the Conjugates seems to 
be that indicated above, a common origin of both sections from 
unspecialised unicellular forms with isogamous conjugation, forms 
which may have lost their motility for a longer or shorter time. 
Mr. West’s view is certainly a possible one, but to speak of “proof” 
is little short of ridiculous. 
The Protococcoideae, always a difficult group to classify, is 
divided into a number of families of which the first is the 
“ Chaetopeltideae ” containing genera, characterised by loose aggre¬ 
gates of seta-bearing cells, regarded in the “ Revision” as reduced 
members of the higher Chaetophorales (Ulotrichales). There seems 
no sufficient reason for separating these forms altogether from the 
typical setiferous types. Of the other families distinguished, the 
“ Protococcaceae (Autosporaceae)” is undoubtedly natural, at least in 
the main. It includes many of the same forms as the Selena- 
straceae of the “ Revision,” the bulk of the motionless freshwater- 
plankton types, often with a curved cell-form, reproducing themselves 
by autospores, often forming ccenobia. Mr. West’s removal of 
