MESOTENIUM, AND SPIROTENIA. 213 
the family, and briefly to trace some of the modifications 
displayed, and to consider how far they bear upon the ques- 
tion. In these we find a certain greater or less amount of 
complexity in the conditions contemporaneous with, and 
subsequent to, the act, which are so constant in their recur- 
rence as, I think, strongly to evidence, when we consider it, 
that the phenomenon is by no means casual or insignificant. 
In the first place, in our genus Mesotzenium the process 
of conjugation takes place by a protrusion and simple fusion 
of the primordial utricles and contents of each pair of cells, 
the parent-cell-wall slipping off in the act, and becoming 
discarded, and finally dissolved. The conjugating cells lie 
in a great variety of positions, and the different zygospores 
are, of course, at first of very varying outlines ; but eventually 
they assume externally a subquadrate or elliptic figure, and 
a proper cell-wall. Again, in Cylindrocystis mutual lateral 
processes of the two conjugating cells are put forth, which 
inosculate, permitting the fusion of the cell-contents of each. 
The isthmus between the two gradually grows wider, until 
the zygospore, from a form somewhat like an H or an X, 
by-and-by assumes a subquadrate outline; eventually, the 
walls of the parent-cells giving way at their suture, and 
becoming by degrees thrown off, the zygospores *having 
acquired a proper cell-wall. In neither genus does the 
zygospore bear spines. In the germination of the zygospore, 
in both genera, there are developed four daughter-cells, each 
of which becomes the primordial individual of a new cycle, 
thus reproducing the species. 
Now, these cases—those of the plants in question, which I 
have thus so briefly alluded to—seem to present the simplest 
conditions in which the phenomenon of conjugation occurs. 
Here the contents of two cells, seemingly morphologically 
equivalent, and apparently of similar value, become fused 
‘ into one, outside either parent cell; and it is at least note- 
worthy that the first result of the fusion of the two distinct 
primordial cells, as, indeed, in all cases of conjugation, is the 
formation of a new cellulose wall round each zygospore pro- 
duced by the act; and this is precisely what takes place 
when the oospore in Vaucheria, Gidogonium, Spheroplea, 
&c., becomes fertilised by the spermatozoids. Likewise, the 
circumstance of the zygospore of Cylindrocystis and Meso- 
tenium producing in germination four daughter-cells has its 
analogy in the same behaviour in the germination of the 
oospore of (dogonium and Bulbochxte—which fact thus, so 
far as it goes, seems to point to the conclusion that in each 
they are the result of a similar act. The daughter-cells, or 
