196 Transactions of the Royal Microscopical Society. 
as seen on former occasions, to the earliest stage of motion, and on 
to the acquisition of flagella. One other slide contained only a 
very few, which did not fully develop, and the other two, so far as 
this form was concerned, were barren. 
This may be taken as a typical example. But we had ascer- 
tained on this and many former occasions that a temperature of 
150° Fahr. (65° ’5 C.), destroys utterly all the adult forms, as well 
as those which had reached any stage of development which might 
clearly be distinguished from the sporule. 
In reviewing the whole series, then, it is plain that rapidity of 
increase and multiplication is the prominent feature in the vital 
phenomena of the monads. Everything subserves this end ; but it 
also appears that the methods by which this prolificness is secured 
are dependent upon the recurrent blending of the genetic elements 
from which each species arises. 
It may be well to compare the results of the whole. 
In the cercomonad division by fission was the constant pheno- 
menon. But this was the division simply of one into two. The 
result of the blending of the sexual elements was the production 
of spores in inconceivable quantities and immeasurably minute.* 
These survived exposure to a temperature of 260° Fahr. (178° C.). 
In the “ springing monad ” the methods of increase were in a 
general sense the same.f In the “ hooked monad ” the increase by 
fission resembled broadly all the preceding ; but it differed remark- 
ably in the fact that the product of the genetic blending was not 
sporules, but minute living forms resembling the parents.^ 
But the “ uniflagellate ” monad multiplied with enormous rapi- 
dity ; not by mere bi-fissipartition, but by multiple fission, as many 
as from thirty to sixty being the product of each fission. § And 
this form, after the union of the sexual elements, poured out innu- 
merable myriads of sporules, so minute that at first they could not 
be seen by our highest powers, but it was merely perceived that a 
mass of something glairy was flowing out of the broken sac, and 
these were afterwards watched unceasingly, and seen in their early 
stages of development. 
Now of these three forms, the two which poured out sporules 
were enabled by their sporules to survive a temperature of 148°'88 C. 
(3U0° Fahr.), but the form which developed living young only feebly 
survived a temperature of 82° '22 C. (180° Fahr.). 
The “ biflagellate ” monad is characterized by multiple fission, 
and in addition a kind of parthenogenetic budding, aiding im- 
mensely in the rapidity of increase, and also the emission of 
minute sporules genetically produced ; and these germs can survive 
a temperature of 121° C. (250° Fahr.), which is exactly the tem- 
* ‘M. M J.,’ vol. x., p. 53. t Ibid., p. 245._ 
X Ibid., vol. xi.,p. 7. § Ibid., p. 69. 
