410 MR. G. S, WEST ON 
eylindrieum is the only known Desnud x which the zygospore 
remains in one of the conjugating cells (presumably the female), 
and the occasional reversion to this type in Hyalotheca dissiliens 
goes far to prove that in all probability this was the ancestral 
mode of conjugation in Desmidiez, and one which has been lost 
by all except Desmidium eylindrieum. Secondly, there is un- 
doubtedly no relationship whatever between the genus Closterium 
and the flagellate Infusoria. 
Having hinted at the probable descent of the Desmidiew from 
filamentous Conjugates, it now becomes expedient to fix upon 
those genera through which this descent could possibly have been 
accomplished, and, after due consideration, the genera Genicularia, 
Gonatozygon, and Cylindrocystis present themselves. I think 
the two former genera may be regarded as but little removed 
from the Zygnemacee ; and although there is much vagueness 
concerning the origin of Cylindrocystis, yet it closely resembles 
the individual cells of certain species of Zygnema*. The main 
line of evolution from Cylindrocystis passed on to the genus 
Penium, an offshoot giving rise to the genus Mesotenium and 
finally to Spirotenia, Some may take exception to the view that 
the genus Spirotenia originated from the genus JMesotenium, 
and be constrained to regard the latter genus as derived from 
the former ; Spirotenia itself being a derivative either of Genicu- 
laria or some filamentous conjugate with a spirally-disposed 
chromatophore. If, however, those species of Spirotenia be- 
longing to the subgenus “ Polytenia” t, in which the chromato- 
phore is cristate, possessing several spiral ridges, be compared 
with certain species of Mesotenium 1, it is seen that a slight 
twisting of the chromatophore is all that is necessary to convert 
such a Mesotenium into a Spirotenia referable to the subgenus 
“ Polytenia.’ Taking this into consideration along with the 
* In the early spring these isolated cells of Zygnema are frequently met with 
in mountain-gatherings, and they bear a striking resemblance to the individuals 
of Cylindrocystis crassa, De Bary, not uncommonly found in abundance from 
the same localities. 
t Sect. Polytenia, Rabenh. Krypt. Flor. Sachs. 1863, p. 178; Turner in 
Kongl. Sv. Vet.-Akad. Handl. Bd. 25, no. 5, 1893, p. 23 (subgen.) ; Liitkemiiller, 
“Ueber die Gattung Spirotenia,” Oesterr. botan, Zeitschr. xlii. 1895, p. 92 
(subgen. Polyrenia). 
t Especially such a species as M, macrococcum, Kirchn. (=M. Braunii, De 
Bary, Conj. p. 74, t. TA. ff. 1-8). 
