ZOOLOGY: S. O. MAST 
215 
This paper however deals primarily with the extent and the accuracy 
of the process of adjustment to the environment, the factors involved 
in it, with its bearing on certain associated problems in behavior. 
Nearly every investigator assumes that the adjustment to the environ- 
ment in an organism serves to conceal it from other organisms. This 
assumption rests upon the further assumption that vision in animals 
is similar to that in man. Thus we have the problem of vision closely 
associated with the question concerning the function of simulation of 
the environment. There are also some other associated problems 
in behavior which are of interest, particularly the one concerning the 
influence of experience on the rate of adjustment. 
1. Extent, accuracy and nature of simulation. Simulation of the en- 
vironment in fishes involves changes in shade, changes in color and 
changes in pattern. Nearly all fishes assume a light shade over bright 
bottoms and a dark shade over dark bottoms, and a considerable num- 
ber assume the predominating colors of the environment, but in only 
a few does the pattern change so as to harmonize with that of their 
surroundings. 
In some of the flounders simulation of the background is probably 
more extensive, accurate, and rapid than in any other animals. Two 
of these forms, Paralichthys and Ancylopsetta, were thoroughly studied 
regarding this response. It was found, in brief, that in glass dishes, 
either on artificial or on natural backgrounds, changes occurred in the 
skin such as to make the animals very closely resemble the background 
in shade, color and pattern regardless of great variations in these respects. 
On a white background they became remarkably nearly white; on gray 
they became gray of practically the same shade; and on black they 
became very nearly black. On colored backgrounds varying from dark 
blue to dark red they assumed colors very similar to those of the back- 
ground in all but the red. On backgrounds having small figures the 
figures in the skin became correspondingly small and on those having 
large figures they became, within certain limits, correspondingly large. 
There is, however, no indication of an actual reproduction of patterns. 
While the size of the light and the dark areas in the background and the 
relative amount of surface covered by them have a profound effect on 
the pattern produced in the skin, their form and special interrelation- 
ship have, within wide limits, no effect. 
2. Rate of adaptation to the background. The time required to pro- 
duce adaptive changes in the skin in Paralichthys and probably also 
in other genera varies greatly. Under some conditions changes result- 
ing in maximum adjustment have been observed to occur in two minutes 
