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IOIO The American Naturalist. [November, 
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posed to be sight, are present in many Infusoria in the form of 
.small aggregates of red or black pigment From such a 
source organs of developed sight can be traced, the subsequent 
additions of retinal nerve supply, humors, etc., having been ob- 
served in animals of successively higher types. Thus we have 
ground for believing in the evolution of this form of special sense 
step by step. 
General sensation is immediately localized on the appearance 
of special organs for its activity. These are the threads and 
bodies, termed nerves and ganglia, which appear first in the as- 
cending scale in the Coelenterata. From the simple structures pre- 
sented by the jelly-fishes we trace the successive evolution of the 
nervous system up to its highest expression in the Mammalia 
and in man. Thus we have the physical basis of the evolution 
of sense-perception plainly before us. The belief in the evolu- 
tion of the more complex forms of perception from simple con- 
Sciousness is therefore inevitable. 
The evolution of ideation may be traced along the lines of the 
affections and of the intelligence. The affections differ among 
themselves in degree of intensity as well as in kind. In their 
simplest form they are mere preferences, or likes and dislikes ; in 
a more pronounced type they are the affections; while in their 
forms of greatest intensity they are the passions. The evolution 
of the emotions is therefore quite comprehensible under the 
direction of use and experience. Profitable use develops strength, 
while experience of the evils of unprofitable use develops restraint 
and disuse. The desires and affections furnish the stimuli to 
action, whence comes experience, and therefore ratiocination. 
Reason, in turn, furnishes material to the affections, and also 
guides them to the accomplishment of their desires. 
It is evident that without consciousness the development of 
ideation would be impossible. Ideation is a result of education 
or the experience of pleasures and pains. The appetites are con- 
scious states, and they furnish, with general and special sensation, 
the basis of the knowledge which animals possess of the material 
world. Granted consciousness, and the progressive development 
of ideation is necessary, except in certain cases where degeneracy 
