170 University of California Publications in Zoology \Vou-9 
two circular window catches, one a third the distance from the 
top and the other a third the distance from the bottom of the 
door. 
The aquarium (pl. 21, fig. 4), after plans by Professor Kofoid, 
in each investigator’s room consists of two stories. The upper 
one is rectangular, with inside measurements of 37 inches in 
length by 17 in width and 13 in depth, and is elevated so that 
its base is + feet 9 inches above the floor. Its walls consist of 
half-inch plate glass 10 inches high and 35 and 14 inches wide 
at the sides and ends respectively, which glass is supported in 
a reinforced concrete frame 2.5 inches thick. The lower aqua- 
rium, rectangular in shape and constructed entirely of rein- 
forced concrete 2.5 inches thick, is of the same length and depth 
as the other aquarium, but about nine inches wider. A wooden 
shelf resting upon concrete cleats is located intermediate be- 
tween the two aquaria and the salt-water system is so arranged 
that small moveable aquaria may be operated thereon. At the 
front base of the upper aquarium is another smaller shelf, sup- 
ported upon iron cleats, which may be used for glassware or 
experimental apparatus whenever desired. It is noteworthy that 
the plate glass of the upper aquarium is set directly into the 
concrete walls, thereby eliminating all metal rods and _ bolts. 
Another important feature is that the upper aquarium backs 
against frosted glass windows, thus making it possible to illum- 
inate the aquarium from any desired direction. The salt-water 
supply pipes are of soft lead with vulcanite cut-offs and delivery 
cocks. Every main angle is provided with a clean-out plug. 
The waste aquarium water is carried away by a system of open 
drains in the cement floor. 
The method of circulation within the aquarium is based upon 
the siphon principle, as follows (pl. 21, fig. 4): From a 1%¢-ineh 
soft lead supply pipe (s) the water enters through a vuleanite 
stopcock into the aquarium inlet (7), which is merely a channel 
7z inch in diameter, in the conerete wall. As the water fills the 
aquarium it also ascends the outlet (0), which lke the inlet is 
a 7-inch channel in the conerete wall, until it reaches an over- 
flow level (1) about three inches below the aquarium top. This 
brings the siphon into action, and the water passing through 
