Life History of Monads. By W. H. Ballinger $ J. Drysdale. 193 
halves become more normal in shape, until the moment when they 
are about to divide; they are drawn at Fig. 8, the nucleus-like 
bodies taking their normal place in each, and often the “ eye- 
spot ” making its appearance. Still pulling in the direction of the 
arrows, complete fission is effected, and each half is provided with 
a sharp “ tail.” Much of this, it is needless to say, was only made 
out after weeks, and in some instances months, of continuous 
labour, and only then with the highest powers. The general 
method of fission, indeed, was made out with the T Vth, with eye- 
piece giving 1200 diameters ; but the complete detail was only 
successfully compassed by the oVth and - 5 - rj th of Powell and Lealand, 
with diameters ranging from 2500 to 5000. 
But even now the whole difficulty of fission in this monad was 
not overcome, for, as we have seen, it is normally provided with 
four flagella ; but at fission these divide into two pairs, so that 
each half of the original monad, although complete in all other 
respects, has only two instead of four flagella. Pet in a very few 
minutes the free halves were seen to have acquired the full comple- 
ment. At first, and for a long time, an inquiry into their mode of 
acquisition seemed hopeless; hut we were at length rewarded by 
seeing the manner in which it happened. The newly fission-formed 
“ calycine,” after darting about rapidly hut irregularly for some few 
seconds, attaches itself to the floor, or to some comparatively fixed 
object, by the free ends of the flagella, and remaining almost motion- 
less itself, a rapid vibratory action is set up for nearly the whole 
length of the flagella, as seen in d, e, Fig. 9. Very speedily the 
ends split, as seen at b and c. This splitting is carried further and 
further towards the base, as seen in b, Fig. 10, where c, d have 
opened out nearly to the end until at length it opens completely, as 
seen in the same figure at a, e. The whole of this process was 
complete in 130 seconds after the pair of flagella became fixed and 
vibratory, and was seen perfectly with the supplementary stage and 
small condenser made by Powell and Lealand for developing the 
markings on Amphipleura pellucida. But it was also seen with 
the usual condenser and the Ajth. 
The semi-amoehoid condition preceding fission appears common 
to all these monad forms before any remarkable vital change. In 
the instance before us it was impossible to predicate whether this 
condition in any “ calycine ” in the field would issue in fission, or 
another vital process in its life history, to which we must now refer. 
Certainly the more frequent phenomenon was mere self-division ; but 
long-continued observation showed in this case, as in others, that, 
although most frequent, it was far from being most important. 
The fact that the semi-amoeboid condition is common to both 
great transformations in this monad, and the one we are about to 
describe is very much the least frequent, enhances the difficulty of 
