1876.] Multiplication by Fission in Stentor Mülleri. 277 
abrupt than in the usual stretched form of the animal when its 
disk is expanded. Figure 16 e represents its appearance at this 
time. 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 Stentor 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 par- 
tially 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 Vorticellz 
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 Vorticelle, such | 
as Vorticella campanula, etc. 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, appar- 
ently 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. Figure 16 f is a sketch of the appearance at this time. 
Suddenly the connection parted, and the two Stentors swam 
Separately away, both assuming the common form of the animal- 
cule when free-swimming, and differing from the original indi- 
vidual only in being of smaller size. 
The complete transformation through all 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. 
1° distinctly marked internal canal or sack 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. 
