SOME PROBLEMS OF REPRODUCTION. 13 
plasm which form the zoospores or gametes ; and the vesicle 
so formed persists and is usually expelled with them. But this 
formation does not always take place, and no share is taken 
by the nucleus in it. A similar vacuolar bladder is formed in 
certain Siphonez. The zoospores vary in number, owing to 
the number of nuclear bipartitions that produce them; the 
smallest (of several sizes, however) and most numerous conju- 
gating exogamously as (facultative) isogametes. Dodel-Port 
relates! that he has seen copulation between small active 
swarmers and larger more sluggish ones, though they usually 
conjugate with those of the same size. So that we have here a 
combination of isogamy and anisogamy. 
CYLINDROCAPSA is oogamous. The oosphere is formed 
simply by the enlargement of a single cell, and is facultative. 
The spermatogonia are formed by the rapid transverse fissions 
of the vegetative cells; and the cell-body of each divides to 
form two spermatozoa. 
CHLAMYDOMONAS PULVISCULUS, referred to above as ani- 
sogamous, shows a transition to the siphonogamy of the 
group we shall next examine, for the gametes come to rest, 
surrounded each with a cell-wall, and the microgamete 
“creeps”’ into the cell-chamber of the megagamete to fuse 
with it therein. 
The Dzsmips, Consueates, and Diaroms are forms perma- 
nently enclosed in their cell-walls, and destitute of cilia or 
flagella, never even forming zoospores. In these conjugation 
is altogether i1sogamous, or in certain Conjugates (Spiro- 
gyra) the male is only distinguishable by its slightly smaller 
size, and by passing, like that of Chlamydomonas pulvis- 
culus, into the megagamete cell-chamber to form the zygote 
therein. In other cases siphonogamy also occurs, but the 
zygote is formed at the junction of the tubes emitted by the 
isogametes. In Diatoms the gametes leave their shells to 
conjugate as naked cells. 
In the Desmid Closterium lunula and certain Diatoms 
1“ Ulotbrix zonata,’ in ‘Pringsheim’s Jahrbiicher,’ vol. x, 1876, 
p. 539. 
