CONCLUSION. 447 
of the last conclusions at which we arrive, is a 
conviction that the greatest and most important 
operations of nature are conducted by the agency 
of atoms too minute to be either perceptible by 
the human eye, or comprehensible by the hu- 
man understanding. 
We cannot better conclude this brief outline 
of the history of fossil Polyparies, extending as 
they do, from the most early transition rocks to 
the present seas, than in the words with which 
These most curious observations throw important light on the 
obscure and long-disputed question of equivocal generation ; the 
well-known fact that animalcules of definite characters appear in 
infusions of vegetable and animal matter, even when prepared 
with distilled water, receives a probable explanation, and the case 
of Infusoria no longer appears to differ from that of other animals 
as to the principle on which their propagation is conducted. The 
chief peculiarity seems to consist in this, that their increase takes 
place both by the oviparous and viviparous manner of descent from 
parent animals, and also by division of the bodies of individuals. 
The great difficulty is, to explain the manner in which the eggs 
or bodies of preceding individuals can find access to each parti- 
cular infusion. This explanation is facilitated by the analogous 
cases of various fungi which start into life, without any apparent 
cause, wherever decaying vegetable matter is exposed to certain 
conditions of temperature, humidity, and medium. Fries explains 
the sudden production of these plants, by supposing the light and 
almost invisible sporules of preceding plants, of which he has 
counted above 10,000,000 in a single individual, to be continu- 
ally floating in the air, and falling every where. The greater 
part of these never germinate, from not falling on a proper matrix ; 
those which find such matrix start rapidly into life, and begin to 
propagate. 
A similar explanation seems applicable to the case of Infusoria ; 
the extreme minuteness of the egg-s and bodies of these animal- 
