202 
PKOGBESS OF MICROSCOPICAL SCIENCE. 
Stentor, the new oral opening gradually enlarging and deepening. 
The slit line between the two disks now disappeared, and at the end 
of another quarter of an hour the upper portion of the body was 
attached to the lower by a connection no thicker than the tail of the 
original had been, though in each the disk was about one-third 
smaller than the original disk, and the slope from it to the smaller 
part of the body below was much less abrupt than in the usual 
stretched form of the animal when its disk is expanded. The oral 
opening of the lower disk was now plainly seen to connect with the 
general internal canal by a circular orifice which varied in size, 
sometimes disappearing as if closed by a sphincter. Up to this period 
of development the Steutor had kept its place, attached by its tail to 
the upper glass of the Wenham compressor, its body stretched at 
great length, its cilia in rapid and vigorous motion, the whole animal 
waving slowly or partially rotating on its longitudinal axis. Now, 
however, it quickly retracted with a spring like the recoil of a bit of 
stretched india-rubber, in the manner common to it and the smaller 
Vorticellse which have long pedicels. The two parts of the body, or 
more properly the twin bodies, enlarged in diameter while shortening 
in length, and it was apparent that the mass of each was about equal 
to the other, although the lower part had been more than twice as 
long as the upper when the whole had been stretched at full length. 
The form of the parts was now almost exactly alike in each, and 
resembled the common bell-shaped Vorticellae, such as Vorticella 
campanula, &c. In the retraction the internal canal, which now 
became plainly visible, also enlarged in diameter when relieved from 
the stretch, and appeared slightly convoluted. It passed out from 
the lower body just below the margin of the disk, and entered the 
upper body at its caudal extremity, apparently having only an 
extremely thin membranous wall at the point of junction of the two 
bodies. These bodies now began a sort of swaying and gyratory 
motion, the lower one still fast to the glass by its tail, and the upper 
one swinging slowly around, the umbilicus between the two becoming 
smaller and smaller as if twisted up. Suddenly the connection parted, 
and the two Stentors swam separately away, both assuming the 
common form of the animalcule when free-swimming, and differing 
from the original individual only in being of smaller size. The 
complete transformation through f 11 the stages I have noted occupied 
about two hours. I did not observe any internal difference of structure 
at the point where the swelling first began. No distinctly marked 
internal canal or sac could be seen when the body was stretched to 
its full length, but the manner in which it became unmistakably 
visible on the sudden retraction before the final separation of the 
parts looked strongly as if it had been there, but was drawn out to 
such tenuity as to be no longer apparent- through the semi-translucent 
body. 
Again, there was no doubt in regard to the fact that the ciliated 
line or slit extending from the disk down the body of the animalcule 
became apparent only after it had been some time under observation, 
and that the length and activity of the cilia along it increased rapidly 
