272 
S. O. MAST 
sible to subject an active amoeba to light without changes of 
intensity owing to the movement of the shadows of one part on 
others in the process of locomotion. 
If orientation in Amoeba is due to changes of intensity as appears 
to be true, it is in principle the same as that in Euglena (Jennings, 
1906, p. 138), Volvox (Mast, 1907, p. 153), and various other 
similar forms. 
REACTIONS IN LIGHT DIFFERING IN WAVE LENGTH 
In these observations the light waves were differentiated both 
by means of color filters and by means of a prism. The filters, 
kindly lent me by Dr. R. P. Cowles, were prepared and spectro- 
scopically tested in the physical laboratory of Johns Hopkins 
University. The red was transparent from 620/xAt out, opaque 
from 450 to 590)Uai and faintly transparent from 380 to 450jjlijl. 
The blue was transparent from 430 to 490jum and from 690^6// out, 
and opaque from 590 to 670/jlijl. The green was transparent from 
380 to 400iUMj from 450 to 550m)U and from OSOai/x out. It was 
opaque between 580 and 660^^ and faintly transparent between 
400 and 450m/z. The following table gives the relation between 
wave-length and color as used in this paper: 
The amoebae, mounted as described above, were studied under 
a magnification of about 150 diameters with very faint illumination 
from the mirror. A beam of direct sunlight which passed through 
8 cm. of water was thrown on the sHde at an angle of about J 
45 degrees with the stage. The organisms were exposed to light j 
differing in color by intercepting the beam with the color filters. 
It was found that amoebae which moved actively in weak diffuse 
light ceased moving shortly after being suddenly exposed to 
Red = 
630 - 760mm 
590 - 630mm 
560 - 590mm 
490 - 560mm 
430 - 490mm 
395 - 430mm 
340 - 395mm 
Orange = 
Yellow = 
Green = 
Blue = 
Violet = 
Ultra violet 
