20 Bulletin Wisconsin Natural History Society. [Yol. 10, Nos. 1 & 2. 
insect from going in a nearly straight path toward the light. Other 
specimens would do the same with only a small part of the lateral 
face of one eye uncovered. In the latter case neither the lightest 
nor the darkest part of the visual field was kept before the eye. 
The insect behaved as if it were not guided by a mere reflex 
response, but had an awareness of the general space relations of 
its region, the relative position of the light and itself and of the 
movements necessary to bring itself toward the light. If such a 
general topographical sense seems too high a psychical endowment 
to be credited to so simple a creature, it must be remembered that 
other insects, notably the bees and wasps have a much more definite 
and detailed cognizance of the topographical relations of their 
environment than anything in the behavior of Ranatra would call 
for. Simple and mechanical as much in the light reactions of 
Ranatra seems to be, there are many features of its phototaxis 
which are very difficult to explain on the basis of simple reflex 
orientation. 
We might expect a priori, to find that somewhere in the course 
of evolution the tropisms become more or less subordinated to 
higher forms of behavior. It is quite evident that much in the 
behavior of animals may be explained as a more or less simple 
manifestation of phototaxis, geotaxis, chemotaxis, and so on. The 
daily depth migrations of pelagic animals is traceable to a consid¬ 
erable degree to variations in the sense of the response to light 
and gravity. One circumstance that leads copepods to swim to 
the surface at night and go down in the daytime is because they 
are positive to weak light and negative to strong light. The nega¬ 
tive reaction of centipedes, termites and many other organisms 
keeps them in dark and secluded situations. The positive reactions 
of many worms and crustaceans to contact stimuli keep them in 
protected situations in various nooks and niches where they escape 
many of their enemies. The positive chemotaxis of many animals 
leads them into situations where they may find their food. 
But one of the chief considerations which makes the study of 
tropisms of such importance is the fact that the tropisms enter as 
components into more complex activities of higher organisms. 
Tropisms in their purity are met with only in the simpler animals. 
As we pass up the scale of life these primary tendencies to action 
become broken up and combined with other forms of behavior, so 
