538 The American Naturalist. [June, 
more than probable that the new rows of cilia are formed at the ante- 
rior end of the adoral zone, which is corresponding with the right or 
aboral end in other groups, for the following reasons: 1. The trans- 
verse rows in the adoral zone are always equal and equidistant, so that 
a new formation between the existing rows is excluded. 2. The fore- 
most rows are short, bearing only a few cilia each ; with the increasing 
size of the animal they become longer, bearing also a greater number 
of cilia, i.e., the adoral zone grows wider, while at the same time the 
number of transverse rows is increasing from about 25 or 30 in all, 
about 18 in front of the peristome, to about 50, or 30 respectively. 
Thus the foremost rows in a small specimen will be about in the mid- 
dle of the processus when the animal has become large. 3, In several 
instances it seemed that the single, shorter, stronger cilium in front of 
the adoral zone (c) was split into two or three filaments, at its end, and 
so it is probable that it represent and grow out into a newly added 
transverse row, the more so as a smaller cilium was often seen in front 
of it, which subsequently would take its place (c’, fig. 4). 
A group of rather crowded, short cilia is at the anterior end on the 
right and dorsal sides, evidently the new additions to the right mar- 
ginal series and the fine, stiff dorsals or “ tactile hairs ” (see figs. 1, 2, 4, 
5, 6). 
Binary fission has not been observed directly. To all probability it 
is going on during retreatment. Many specimens have been rather 
closely observed during several—up to four—days in succession with- 
out any changes indicating fission being noticed on the anterior part, 
except in size and the number of adoral transverse rows. Lately two 
animals were seen, side by side, growing to a large size, during three 
to four days. Both of them were in normal shape, at noon, one day; 
when seen again, about an hour and a half later, both had changed : 
the anterior part was shorter and smaller, the end looked as though 
chopped off, the number of transverse adoral rows was only about 18 in 
front of the peristome; the cilia were short and showed that peculiar, 
slow vibration always seen on new cilia during and just after fission in 
Oxytrichide and all ciliates bearing an adoral zone. Evidently they 
had undergone transverse fission, On the following day both specimens 
again presented a different appearance (fig. 6): the anterior end was 
a fan when spread out,- In innumerable instances this was distinctly seen in 
many species of the different groups named, while the animals were living andin 
normal condition. Whether the cilia in the transverse series are always separ 
ated down to the base, or are coherent so as to forma kind of short ‘‘ mem- 
branelles,” may still be an open question. 
` 
