596 Cain PInG 
In an aquarium with several larvae at the bottom, a piece of narrow 
board was placed at an angle of 60° with its upper end_ projecting slightly 
above the water. About an hour later two larvae had climbed to the 
top of the board, three were halfway up the board, and one was starting 
to climb. An electric light was then turned on and held about 13 centi- 
meters directly above the water surface. All except one of the larvae 
started to go to the bottom. Then the light was turned out. At the 
end of an hour two larvae were climbing again, one of which was 
very close to the surface of the water. In repeating this experiment 
several times, whenever no light was hanging there the larvae steadily 
climbed toward the surface. Sometimes even after the light was turned 
on, they refused to go down but hid themselves in shade on the lower 
side of the board or under some floating leaves. The writer has frequently 
noticed that in the pools under the sun’s direct rays the larvae hide 
themselves under floating boards, scums, and the like, in order to stay 
nearer the surface. 
Mechanical injury.— The larva has been found incapable of regenerating 
any part lost from its proleg or caudal process. Cutting.off the respiratory 
spiracles interferes with the normal process of respiration. Owing to 
the amount of air stored in the richly ramified tracheae, the larva is able 
to live for a short time. In one instance the larva died soon after one 
of the oral lobes was snipped off. 
THE PUPA 
Pupation and perching habit 
When the larva is ready to pupate, it approaches some object and 
grasps an edge with its sixth and eighth pairs of prolegs. At this time 
it ceases its activities in feeding and swimming, the larval skin gradually 
hardens, and the wrinkles on it disappear. Its color becomes darker and 
darker, until it is homogeneously brown. The head region, including the 
first four segments, becomes depressed or slightly concave on the dorsal 
side and convex on the ventral side. Thus the outline resembles that 
of a shovel, but it is slightly narrowed toward the anterior end. The 
pupa perches rigidly on its support (Plate LVII, 43), secure for the 
transforming period. It is hard to remove it by jerking or shaking. 
A great number of pupae may be found perching side by side on a stick, 
