Life Eislory of Monads. By W. H. D ailing er ^ J. Drysdale. 195 
well defined as exquisitely minute oval bodies, highly refractive, 
with a power of 2500 diameters (sV). This is drawn at Fig, 16. 
The future of these minute bodies was carefully followed with 
the -gVth, and large numbers developed under examination, the 
development being distinctly traced in all its stages. First the 
minute and just perceptible specks appeared to swell — to grow 
larger in all directions, but they were perfectly inactive. This 
continued for from two to three hours, when some of them began to 
have a beaked appearance, as shown at a, h, Fig. 17. Growth was 
now very much more rapid, and at the end of two hours more they 
had assumed the shapes shown at Fig. 18. Between this time and 
the end of the next hour, in some way which we entirely failed to 
elucidate, flagella were acquired ; in some cases two, but in the 
majority three, were made out, but never more at this stage. They 
now became rapidly motile, and of course the difficulties of noticing 
minute development increased ; but their appearance thirty-fiive 
minutes after the acquisition of the flagella is drawn at Fig. 19, 
the nucleus-like body having definitely appeared. From this time 
they grew rapidly, and in many the four flagella could be seen ; and 
at the end of the ninth hour after emission they had taken the 
parent form, and in all save size were the well-known " calycine,"' 
which had so long occupied our attention. Their aspect in this 
Btage is drawn in Fig. 20. 
The complete life history of this monad is therefore, — develop- 
ment from a germ or sporule of extreme minuteness, and on the 
attainment of maturity multiplication by fission, constantly and for 
an indefinite time ; but the vital power is at intervals renewed by 
the blending of the genetic elements, effected by the union of two, 
when both are in an amoeboid condition, from which a still sac 
results, in which germs or sporules are formed, which eventually 
escape, and again originate the life cycle. 
We now proceeded to make the usual experiments on tempera- 
ture, and its effect on the adult and the sporule. Our method has 
already been minutely described,* and in this case, as in all the 
others, was strictly followed. The result showed that the sporules 
of the *'calycine" can resist a temperature of 250° Fahr. (121° C), 
but no higher. We may quote one example in illustration. Six 
slides were taken, the contents of which were fully ascertained to 
be what was needed. They were heated in the usual way up to 
250° Fahr., and allowed gently to cool. The contents were then 
examined with our best powers, first dry and then moist, but no 
trace of motion — even Brownian — was visible in any one instance. 
But in twenty-two hours from the time of heating three of the 
slides had a number of " calycine " forms in a very advanced stage, 
which had been watched from their origin in still gelatinous points, 
* 'M, M. J.; vol. X., p. 57. 
