32 IOWA STUDIES IN NATURAL HISTORY 
an aperture at the top 2.5 em. wide and 6 em. from the other 
end, so placed that its lower border was 2 em. below the sur- 
face of the water, was placed approximately 15 em. from the 
first. The third partition (In), with an aperture at the bot- 
tom 2.5 em. square and near the middle, was placed just far 
enough from the end wall of the aquarium toward the sun to 
include all of the shaded area. 
Without the partitions in place one of the larvae was placed 
in the aquarium at the unshaded end and permitted to seek the 
shaded area three times in succession. The partitions were 
then put in place, the larva placed in compartment 1 at the un- 
shaded end of the aquarium, and the time noted which was re- 
quired for it to reach the shaded area in compartment 4, after 
it had passed through the aperture in the first partition. This 
was repeated twice. All the other larvae in the series were 
treated in the same way; consequently, each animal was allowed 
to pass through the maze three times in each experiment. These 
animals were kept in individual aquaria, and individual records 
were kept for all of them. Following the initial experiment 
two days intervened before they could be repeated. They were 
then repeated on six successive days. Three days again inter- 
vened after which the experiments were repeated on the 12th, 
14th, 15th, 19th, 20th, 21st, and 22d days. The record includes 
the time required for each animal to pass through the maze in 
each of three successive trials on every day on which the ex- 
periments were made. ‘However, on the 8th day larva No. 5 
became sluggish by reason of its approaching metamorphosis 
and was discarded. On the 19th day larva No. 1 also became 
sluggish and was discarded. Consequently, after the 8th day 
the series includes only five, and after the 19th day, only four 
animals. Curve AC, fig. 2, represents the averages of the three 
trials of all the animals in the series on the days on which the 
experiments were made. It indicates a decided drop from the 
initial interval of 118.3 sec. to 89.9 sec. on the 5th day. After 
this there is considerable variation in the time interval re- 
quired, but it does not again rise higher than 99.1 sec. After 
the 15th day there is again a decided drop until a low point of 
39.1 is reached on the 21st day, although three days intervened 
- after the 15th day until the next series of trials was made. 
