MESOTANIUM, AND SPIROTHNIA. 211 
being, im fact, but two ordinary, in no way previously special- 
ised, joints of the filament.* 
In CGidogonium, varied as are the conditions between mo- 
neecious, gynandrosporous, and dicecious, under which the 
essential elements concerned in the reproduction present 
themselves, there seems to be still less difference, on the 
whole, in form and size of the spermatozoid and the oogonium 
themselves, than in the other cases adverted to. 
In dogonium curvum but one spermatozoid is formed in 
each antheridium-cell, and, like the oospore, it is globular ; 
and although there is a considerable difference in size between 
the two, in this respect they much more nearly approach than 
in the previously cited cases; that is, though, of course, equally 
physiologically distinct, they are more nearly morphologically 
equivalent. In Gdogonium Cleve has shown that the oospore 
in germination produces, by segmentation of its contents, four 
daughter-cells, which become ciliated, and swim away as 
zoospores to reproduce the species;+ while for Bulbochete, 
whose fructification is gynandrosporous, Pringsheim had pre- 
viously shown that here also four daughter-cells are developed 
from the oospores, which become zoospores, and reproduce 
the plant. 
These, then, are unquestioned and unquestionable instances 
of a true generative act. It would be useless, as regards the 
subject under consideration, to travel out of Confervoidze for 
further illustrative cases where a true reproduction is effected 
by spermatozoids and oospores, because we should be unne- 
cessarily receding in the system from Conjugate. 
Now, in the cases which I have just so briefly alluded to, 
more or less varied as may be the accompanying conditions, 
simple or complex, or more or less specialised as may be the 
accessory organization, the one pervading essential circum- 
stance in the phenomenon beyond doubt seems to be the ma- 
terial union, the flowing into one, the simple fusion, of at 
least two primordial cells. 
Now, what /ess than this is the act of conjugation in our 
Cylindrocystis and Mesoteenium ? 
It may be, perhaps, answered that neither of the two con- 
jugating cells is ciliated, and that they are apparently mor- 
* Cohn, ‘ Berichte der Berl. Akad.,’? 1855; also ‘Ann. des Sciences Na- 
turelles,’ 4 ser., vi. p. 187 ; and ‘Ann. Nat. Hist.,’ 2 ser., vii. p. 81. 
+ Cleve, “Iakttagelser 6fver den hvilande Gidogoniums-sporens utveck- 
ling,” in ‘Ofversigt af Kongl. Vetenskabs Akademiens Forhandlingar,’ 
Stockholm, 1863, p. 247. 
+ Pringsheim, ‘ Beitrige zur Morphologie und Systematik der Algen,”’ 
in ‘ Jahrbicher fiir wissenschaftliche Botanik,’ Band i, p. 55. 
