94, C. CLIFFORD DOBELL. 
be most easily described, I think, by recording a typical case 
(see Pl. 4, figs. 11-16). The first thing to be seen is the 
approach of two monads to one another. Hitherto they have 
been swimming about apparently at random, but they now 
draw near and come in contact by their anterior ends (fig. 11). 
Each monad appears to be normal, possessing one nucleus, 
reservoir, etc. For afew moments they swim about merely 
touching one another, and gliding over one another to some 
extent. But it is soon seen that an actual adhesion is 
taking place, so that the monads become firmly united at their 
anterior ends. Both the flagella continue to move actively, 
and very often get entangled. 
After swimming about for some minutes in this manner it 
can generally be made out that one of the flagella is becoming 
shorter. At the end of a quarter of an hour this is usually 
very evident, and a little later, or perhaps even now, one 
flagellum is completely drawn in. Fusion is extending back- 
wards, so that the conjugants have the appearance of one 
large, bilobed monad, rather than of two applied to one 
another (fig. 12). Active movements still occur, and further 
fusion is seen slowly to be taking place. In about half an 
hour more the monads present an appearance hke that seen 
in fig. 15. It appears as though one monad absorbs the 
other; for a little later they have the appearance, shown in 
fig. 14, of one monad bearing a projecting process on its side. 
Still later the fused individuals present the appearance of one 
somewhat asymmetrical organism (fig. 15), only differing 
from the ordinary monads in being slightly bilobed at the 
posterior end. Sooner or later the remodelling is completed, 
and an organism exactly like an ordinary monad is formed, 
though it is usually noticeably larger, and sometimes can be 
seen, after careful examination, to contain two nuclei in place 
of the usual one. 
The subsequent history of these binucleate monads is not 
always the same. Development may proceed along one of 
two lines: (1) The animal may encyst, or (2) it may continue 
to feed and divide longitudinally, just like an ordinary indi- 
