G. H. F. Nuttall 
177 
about two minutes. When left quiet and exposed to the light, they 
retreated beneath the cloth or along its shady border; they walked away 
from the light, or, when the cloth was sufficiently near (ca. 3 cm.), 
toward the light, to gain the shady side of the cloth. Gorged lice 
exposed to strong light run rapidly to darkness (see p. 100). 
Effect of light on development. The following experiments were 
carried out so as to determine if light exerts any effect on the 
development of lice {corporis). 
The insects were fed twice daily upon the arm and, between feeds, 
they were kept at 31° C. in an electrically heated thermostat with 
double glazed doors facing a large window through which strong day¬ 
light penetrated in summer (July 1917). The lice were confined in 
glass vessels provided with a white background and each containing a 
hair-grid upon which eggs were laid and the lice clung. This arrangement 
prevented the insects from having access to any shade other than the 
small amount afforded them by each other’s bodies when aggregated in 
masses. After the females had laid the desired number of eggs on the 
hair, they were removed; the eggs and larvae which issued therefrom 
were maintained in. the light, nights excepted, until they attained 
maturity. By way of control, other lice, the progeny of the same 
adults used in the light experiment, were raised in the dark in the 
same thermostat under otherwise identical conditions. 
Exposed to the light: 
( a ) 3 (J 5 ? laid 103 eggs of which 85 (83%) hatched. From 
the 85 1st stage larvae were raised 30 adults (35%), the rest 
failing to reach maturity. 
(b) 4^4$ laid 89 eggs of which 63 (71%) hatched. From the 
63 1st stage larvae were raised 24 adults (38%), the rest 
failing to attain maturity. 
Controls kept in the dark: 
(c) 2 d 5 $ laid 107 eggs of which 101 (94%) hatched. From 
the 101 1st stage larvae were raised 38 adults (37%), the 
rest failing to reach maturity. 
(d) 4 d 4 9 laid 93 eggs of which 84 (90%) hatched. From the 
84 1st stage larvae were raised 29 adults (34%), the rest 
failing to attain maturity. 
The results obtained in the above experiments show that daylight 
does not apparently exert, an inhibitive effect on the development of 
corporis. The number of adults raised from first stage larvae in the 
light and in the dark was about the same. Although the percentage of 
Parasitology x 12 
