114 University of California Publications in Zoology (Vou. 9 
figure D and plate 16. It has the form of an elongate, truncate 
pyramid, which is lined with heavy asbestos paper, and contains 
at its lower end the heating lamps. These are connected with a 
regulator to be described presently. The space between the 
double walls is filled with cotton, except at the front where the 
space communicates below with the chamber where the lamps 
are, and above with the space between the two plates of glass 
which form the front wall of the upper box. The latter space 
in turn is connected at the peak of the roof with the interior of 
the box. Consequently air warmed by the lamps rises, filters 
through the net floor, envelopes the apparatus, and passes out 
above, whence it descends between the front walls to the lamps. 
There is thus a constant circulation preventing the accumulation 
of hot air above and cold below. 
The heating apparatus consists of four 32-candle power in- 
candescent lamps arranged in two pairs. The members of each 
pair are connected in series. As a result they do not burn with 
maximum brightness and heat, and they therefore use less 
current. One pair is directly connected to the source of the 
current and burns constantly, the other pair is controlled by the 
regulator. 
The regulator, which lies entirely within the box, is made on 
the plan devised by Mast (1907). The tube of the regulator is 
suspended at the highest part of the box. It runs lengthwise (figs. 
D and E and pls. 16 and 17), bending back on itself several times. 
At the left end (figs. D and E and pl. 17) the tube turns down, 
ending in a U-bend filled with mercury (mer., figs. D to F). 
The greater part of the tube is filled with glycerine (glyc.), its 
escape being prevented by a cork stopper visible in plate 16, 
upper figure. The shape of the glycerine-filled part is immaterial. 
However, the longer it is, the thinner the glass, and the smaller 
the diameter, the more sensitive is the regulator. The rest of 
the regulator in its simplest form is shown in figure F. 
On the free end of the mereury-filled U-tube is fitted a cork 
(cork). The cork is pierced by two heavy wires (lr. wr. and 
ct. wr.), at the lower ends of which are binding posts.- The upper 
end of one (lr. wr.) is bent at right angles (figs. G and H) and 
passes through one end of a short lever (/r.) made of a piece of 
