416 Proceedings of Royal Society of Edinburgh. [sess. 
series — on another slide two had been set aside, which on 
the following day were found to be still, in a sense, the same 
number. Yet evidently one of the creatures had begun to divide, 
but stopped in the process, so that while on the slide there was 
one normal form, the other was a monster, composed of two full- 
grown Paramecia with organic union between the anterior part of 
what should have been the posterior daughter and the posterior 
part of the anterior one. There was no constriction between the 
two, or other hint of their origin. The two bodies formed one 
continuous whole with one circulation, and was so flexible through- 
out that the two extremities could touch. On the 17th of May 
it appeared, and on the 18th was in no way changed. On the 
1 9th the slide on which it was isolated contained three forms : 
the monster had given off a daughter from either end. These 
daughters were ordinary P. caudatum of good average size; they 
continued to divide by themselves, and in every way appeared to be 
normal. On the 20th the monster remained as it was, but again 
on the 21st it repeated the operation of giving off a daughter 
from either end. On the 22nd it had not multiplied, but on the 
23rd for the third and last time it had given off a daughter from 
either end. These last, however, were markedly smaller in size, and 
otherwise like the “aurelian” daughters that had been given off by 
the cleft-tail individual. Previous to this the posterior creature 
had gradually been becoming inclined at an angle to the anterior 
one. Up to this point the combined activity of the monster had 
been as great as that of any normal Paramecium. The anterior 
half, perhaps naturally, was the more active, and, in a sense, the 
guiding part. Its cilia were feverishly active : they were also 
longer and better developed, especially in the anterior regions, than 
those of the posterior creature. This greater anterior activity may 
also have found expression in a process that began to come off 
from it a little above the angle made with the posterior form. 
Further, the two contractile vacuoles of the anterior creature 
were close together and contracted simultaneously. From the 23rd, 
i.e ., about a week after its appearance, growth ceased to show 
itself, as we have seen, in the regular separation from either end 
of two daughters on every second day, and began rather to express 
itself in the growth of the aforesaid process and in remarkable 
