594 VICTOR E. SHELFORD 
b. Discussion of the parallel statements. (11) Animal (or 
motile organism) distribution at any given time is a better in- 
dex of the condition at’ that time than the distribution of plants, 
because when the conditions at a given point become unfavorable, 
the animals (or motile organism) move to another situation, while 
the plants (or sessile organisms) remain or die. 
(V) The fifth is not well established. However, a prelim- 
inary testing, for example, of the rheotaxis of a arge number of 
brook animals has shown them to be strongly positive, strong 
positive rheotaxis being a common behavior character. Many 
of them have special means of attachment which may be brought 
into play with great speed. 
The darters are strong swimmers and are able to live in rapids 
by virtue of their swimming powers and positive reaction, while 
the snails (Goniobasis) which occupy similar situations, are able 
to maintain themselves because of the strength of the foot and 
positive reaction. The two are ecologically equivalent. The 
sixth statement appears to be generally true, but needs experi- 
mental confirmation. 
The proposition may be summarized as follows: The behavior 
and general mode of life of animals are the superficial equivalent 
of the structural phenomena in the vegetative parts of plants. 
Behavior and vegetative structure are convenient indices of 
physiological conditions within the organism. 
To illustrate this still further, let us consider the plants of the 
sand areas at Chicago and in Manitoba. As compared with 
Chicago plants, the plants of Manitoba differ in size and structure 
under the more arid conditions found at the point where Criddle’s 
studies were made. The Manitoba tiger beetles do not, so far 
as I can find, differ from the Chicago forms in any of the struc- 
tural characters which have to do with their meeting those condi- 
tions, but they dig their holes deeper and require longer time for trans- 
formation. The tiger beetles of the desert and semi-desert and 
the tropical sand areas (Batesand Westwood, ’52; Snow’77; Lucas, 
83) are usually nocturnal or crepuscular; those of moister and 
cooler areas are diurnal—a differencein behavior. Desert plants 
are structurally adapted to withstand the desert conditions 
