524 
CLIFFORD DOBELL. 
Division is, in all cases which I have observed, an equal 
binary fission, resulting in the production of two small 
organisms exactly like the parent organism in everything save 
size. Although the organisms which are about to divide are 
usually of large size, this is not always the case. I have seen 
a number of quite small forms in various stages of the pro- 
cess. Again, most dividing' organisms are filled with food- 
bodies, but this is not always so. Illustrations of this will 
be found in the figures. 
During’ division the animal remains at rest, with all its 
pseudopodia completely retracted. Not until the two 
daughter-organisms are completely separated do the pseudo- 
podia again make their appearance. I believe, moreover, that 
the animal is always attached to some substratum during 
division; that is to say, it does not divide while floating 
freely in the water. I infer this from the fact that I never 
obtained any division stages in organisms suspended in the 
water ; whereas I obtained many in the organisms attached 
to cover-glasses floating on the surface film or placed at 
various levels in the aquaria. Most of the dividing organisms 
were found attached to the surface film. 
The nucleus divides by mitosis, the centroplast playing 
the part of a centrosome. The whole process can really be 
seen at a glance by inspecting the figures (PI. 27, figs. 8-22), 
but the following brief account may be given in amplification. 
Pro phases. — The centroplast is the first organ to divide. 
Immediately before division it is in the “ typical” condition 
(PI. 27, fig. 5), displaying a large central granule and a 
distinct membrane. It then becomes elongated, and the 
central granule divides into two (PI. 27, fig. 7). In the early 
stages of division the central granule appears (see PI. 27, 
fig. 7) as a minute cylindrical body with two deeply-stained 
polar caps — presumably halves of the original granule. A 
little later, however, the caps become minute spherical 
granules, connected by a deeply-staining strand (PI. 27, fig. 8). 
This appearance is exactly comparable with that of a dividing 
.centrosome, at the stage when the daughter-centi osomes are 
