118 University of California Publications in Zoology |Vou.9 
the cell. Just outside the shelf a triangular deeper depression 
(dep.) is ground in the glass. At the outer angle of the depres- 
sion a small hole (c), about 1 mm. in diameter, is bored through 
the glass and is connected by an outlet channel (out. ch.) or 
eroove ground in the under side of the slide with another larger 
hole (d) leading to the upper side. At the opposite end of the 
cell three small grooves lead from the cell to a hole (b) which 
is connected by an inlet channel (in. ch.) with the hole a. The 
inlet and outlet channels on the under side of the slide are 
closed when the two slides are bolted together. Similarly the 
depression, shelf, cell and grooves on the upper side are closed 
when a cover-glass is placed in the position indicated by the 
coarse dotted line. Perfectly tight joints are ensured by thin 
films of vaseline encircling the inlet and outlet channels below 
and the cell and connected parts above. All parts are easily 
accessible for cleaning. (3) Fluid is conducted to the slide by 
means of glass capillary tubes (cap. tb.) and from it by both 
glass and rubber tubes. The capillary tubes are supported and 
connected with the slide by two tube-supporters (7b. sup.) made 
of short, thick-walled, tapering tubes of glass. The latter are 
ground into the holes a and d and fit firmly and tightly. As 
they do not extend entirely through the slide (see fig. J), they 
freely communicate with the inlet and outlet channels. All 
joints of the tubes, while very nearly tight, may be made com- 
pletely so with bits of melted parafin. 
The inlet capillary tube is dipped into a bottle, as shown at the 
right in figure K ; the outlet tube is connected with a waste bottle 
by a small rubber tube which passes through a pinch-cock. The 
air of the waste bottle may be exhausted through another tube 
which passes out through a hole in the back of the box (pl. 16), 
and a current of fluid caused to flow through the cell. By having 
the waste bottle lower than the supply, the current once estab- 
lished becomes continuous, as a siphon, and may be accurately 
regulated by the pinch-cock. The glass must be chemically clean 
in order that the fluid may be started through without leaving 
air bubbles behind. Something of the arrangement of the slide 
and the accessory parts can be seen in plates 16 and 17. 
Tt will easily be seen that fluid after entering the cell can 
