Dr. Dobell on the Influence of Light on the Growth of Animals. 459 
March 20th, 1859.—A number of ova of the Silkworm (Bombyx 
mori), all of the same age, were placed in each of the two cells. No 
change was observed until May 18th (sixty days after the commence- 
ment of the experiments), when one larva emerged from the ovum 
in each cell ; and during twelve days, larvee continued to emerge in 
the light and in the dark at the same rate. 
June 9th.—Sixteen larvee, as nearly as possible of the same size, 
were selected in each cell, and the rest removed. The experiments 
then proceeded with these thirty-two individuals, and no death 
occurred from first to last. 
The following Table shows the day on which each larva began to 
spin ; the day on which the perfect insect escaped from the pupa; 
and hence the number of days occupied by the metamorphosis. 
Light. Darkness. 
Day of Day of Number of days Day of Day of Number of days 
beginning | escape of | occupied by meta- || beginning | escape of | occupied by meta- 
to spin. | the Moth. morphosis. to spin. | the Moth. morphosis. 
July 1 | July 18 {18 days inclusive|| June 30 | July 18 |19 days inclusive 
” 2 ” 19 18 ” ” ” 30 ” 18 19 ” ” 
” 2 ” 19 18 ” ” ” 30 ” 18 19 ” ” 
» 2 | » Wilt , » » 30) , 18/19 , » 
n 2 » AS |17 yy » 30) ,, 21/722 , 4 
” 2 ” 19 18 ” ” July 1 ” 18 18 ” ” 
” 2 ” 19 18 ” ” ”» I ” 18 18 ” ” 
” 3 ” 19 17 ” ” ” 2 ” 18 17 ” ” 
” 3 ” 21 19 ” ” ” 2 ” 19 18 ” ” 
” 4 ” 20 17 ” ” ” 2 ” 20 19 ” ” 
” 4 ” 20 17 ” ” ” 2 ” 19 18 ” ” 
” 4 ” 20 17 ” ” ” 2 ” 20 19 ” ” 
” 4 ” 21 18 ” ” ” 2 ” 21 20 ” ” 
” 4 ” 21 18 ” ” ” 3 ” 21 19 ” ” 
» 5 ” 21 17 ” ” ” 3 ” 20 18 ” » 
” 6 » 24 )19 ,, ” | ” 4 » 21 {18 ” ” 
From this it is seen that the mean period occupied by the meta- 
morphosis in the darkened cell was eighteen days fifteen hours, and 
in the light cell seventeen days sixteen hours. 
The longest and shortest periods in the darkened cell twenty-two 
days and seventeen days, in the light cell nineteen days and seven- 
teen days. 
June 9th.—On selection of sixteen of the largest larvee from the 
inhabitants of each cell, it was noted that, when sixteen were selected 
from the darkened cell and several of similar size removed, only 
four could be found as large in the white cell, the remaining twelve 
selected were therefore of a rather smaller size. This difference in 
the two cells became less obvious afterwards, but, throughout the 
experiments, there was a slight difference of size in favour of the 
darkened cell. 
With these exceptions, no difference could be detected between the 
results obtained in the cell from which light was completely excluded 
and in that exposed to its full influence. 
The larvee, the silk produced, and the moths from the two cells, 
