SOME OBSERVATIONS ON ACINETARIA. 653 
the embryonic mass which contains the greater part of the 
nucleus of the parent. This embryonic mass gives rise to 
usually about six to eight oval blocks measuring about 46 1 
long, by about 14 wide, which develop cilia and swim 
actively about in the brood pouch. 
A rather small proboscidiform individual was found to 
contain six large active ciliate embryos at 5.45 p.m., and at 
8.35 p.m. one of these measuring 46 jz long was seen to show 
signs of a division, which was complete by 10 p.m., the two 
products of the division measuring 244 long. By the next 
morning all the embryos in the brood pouch had divided. 
Just before the ciliate embryos escape, they exhibit parox~ 
ysms of activity, during which they swim over and over each 
other in the brood pouch, these periods of intense activity 
being interspersed by long rests, during which the cilia beat 
very languidly. 
In the case of a small proboscidiform individual, of which 
the six embryos were very active at 3.30 p.m., they broke 
through at 5 p.m., measuring 28 « long by 144 by 104. On 
the other hand, a large proboscidiform individual, seen at 
4 p.m. to contain a large number—over 30—of active embryos 
which escaped at 4.50 p.m., and which measured 20 by 10 
in the stained preparation. These embryos were fixed at 
once, and one of them is figured (Pl. 15, fig. 11). 
The embryos seemed always to escape from a lateral 
opening not far from the animal’s point of fixation. Nearly 
all the cytoplasm and nuclei is used up in the formation of 
the embryonic masses, and in most cases in which an indi- 
vidual contained a large number of embryos, the parent, after 
the escape of the embryos, is left a mere shell which soon 
perishes. ‘he free embryos are more or less oval animals 
with a decidedly flattened ciliated ventral surface, and a 
convex dorsal surface. On the animal’s left side there seems 
to be a flap overhanging the ventral surface. In the ventral 
region there are large vacuoles which often contain nemato- 
cysts, and there is a single small contractile vacuole. They 
move in a curious hesitating manner with the narrow end 
