PHYSIOLOGICAL ANIMAL GEOGRAPHY 
593 
TABLE 11 
a Comparison of the responses ‘of (motile) animals and (sessile) plants 
ANIMALS (MOTILE) 
PLANTS (SESSILE) 
I. Animal behavior is evident be- 
cause of motility: 
II. When an external stimulus is ap- 
plied to an animal, it responds 
mainly by movements which are 
usually more or less random, 
and which bring the organism 
into various conditions, one of 
which relieves the disturbance 
and the organism resumes nor- 
mal activity, in conditions 
which brought the relief. These 
conditions are not necessarily 
advantageous. (Jen- 
nings. ) 
III. Animal behavior is usually plas- 
tic, 1.e., may be modified by 
external stimuli, but some- 
times appears rigid. 
IV. (Animal structure is only slightly 
plastic. 
occurs in the early stages). 
Structural modifications 
rarely of importance in the life 
of the animal. 
V. The motile organisms of a given 
habitat usually have common 
behavior characters. Com- 
bined structural and behavior 
characters of comparable forms 
of a given habitat, or of similar 
habitats are ecologically equiv- 
alent.® 
VI. The breeding activities of ani- 
mals are probably least modifi- 
able and least regulatory, but 
are governed by the same laws 
as the other activities. 
LOLs Odep 410))e 
The plasticity usually | 
are | 
(Shel- | 
I. Plant behavior is inevident be- 
cause of lack of motility. 
II. Plants respond more evidently 
through changes in form and 
structure. 
III. Plant structures are usually plas- 
tic but frequently appear rigid. 
IV. Structural modification of plants 
is often of importance in the 
life of the plant. 
V. The plants of a given habitat 
usually have common structure 
and functions, or those that 
are ecologically equivalent.® 
VI. The reproductive organs and em- 
bryonic stages of plants are less 
modifiable than the vegetative 
stages of adults. 
§’ The meeting of the same general conditions in a different way constitutes 
ecological equivalence. 
The term was first used by Cowles. 
