Hazen: Lire History or SPHAERELLA LACUSTRIS 295 
Since, therefore, microzooids of Sphaerella are formed un- 
der the conditions which Klebs found were necessary for the 
production of the sexual cells in the closely related genus Ch/amy- 
domonas, viz., lack of nutriment and presence of light, the assump- 
tion that they are potentially gametes appears to be justifiable. If 
no conjugation really takes place, its absence may be accounted 
for by the fact that in the successive conditions of activity, slow 
growth, and rest, a sufficient opportunity for rejuvenescence is found. 
THE SO-CALLED CONJUGATION OF MEGAZOOIDS 
Velten (71) has described and illustrated with considerable 
detail a process which he considered conjugation of megazooids. 
This does not differ essentially from cases which I have frequently 
observed. Two zooids are found attached together by their 
posterior ends: (Fig. 42) and the content of one cell passes over 
into the other (Fig. 43), the cilia of each cell meanwhile keeping 
up active movement, at least for a part of the time. Finally a 
spherical zygote is produced which does not differ from the ordi- 
nary resting-cell (Fig. 44), the fate of which Velten did not learn. 
I have not been able to get any further development from such a 
product of fusion by cultivating it in a Van Tieghem cell. 
Rostafinski (’75) rejects Velten's interpretation of this phe- 
nomenon on the ground that it is contrary to all previous ob- 
servations, in that not microzoospores, but megazeospores con- 
jugate, and by their posterior ends instead of by the ciliated points. 
So far Rostafinski's objection holds good ; but when he goes on to 
say that Velten's conjugation is to be interpreted as a case of a 
parasitic monad swallowing a zoospore of Chlamydococcus, I think 
he is entirely wrong, for the cases (cf. Figs. 39-44) I have ob- 
served admit of no such explanation. On the contrary, I think 
they are cases in which the original division was incomplete and 
the two-headed monster, after struggling in vain to complete the 
separation, fuses again to form one cell. This interpretation re- 
ceives support from one case where I observed the actual for- 
mation of such a monstrosity. When the division had reached 
a stage similar to that shown in Fig. 47, the mother-cell-wall 
burst and one perfect zooid escaped while the rest of the cell-con- 
tent issued forth in the form of a large ciliated mass with a smaller 
