OR FRESH WATER POLYZOA. 61 
or false tongue above the mouth, being only a fold of the 
disc, is hollow. The nerve-mass retreats into this cavity 
at will, probably by means of minute muscular fibres ; and 
in this position, also, seeks security from injurious pres- 
sure, while the polyzoén is crowded within the shelter of 
its cell. Thus the epistome, in addition to its other mul- 
tifarious uses, serves at times as a brain box. 
The organs of digestion hang from the disc above, oc- 
cupying the centre of the tube, and floating freely in the 
rapidly moving blood (fig. 5, K, K’, K”). The throat is 
closed at the lower end by a valve (fig. 5, K”), which 
opens into a gourd-shaped sack, the stomach; close 
by this is another valve which opens from the stomach 
into the intestine (fig. 5, K™ )- The last is a canal 
leading up, side by side with the throat, for a short dis- 
tance, but finally bending away from it, and opening ex- 
ternally through an aperture in the pellucid tube, just 
below the base of the ruffle, and not far from the mouth 
(fig. 5, K), 
Though the walls of these organs are variously tinted, 
they are not opaque, and, therefore, while not interfering 
materially with the view through the clearer substance of 
the tube, add greatly to its beauty. The yellowish throat, — 
the stomach striped with dark brown, and the intestine, 
also dark brown, form a colored axis, giving a lifelike 
warmth to the airy delicacy of the surrounding film. 
We have seen by what strange methods the food is 
captured, but this is not more curious than the way in 
which it is digested. A throattul, for we cannot say 
mouthful, is no sooner admitted to the stomach, than it js 
rolled up and down from one end to the other, with great 
violence. The walls of this organ take on a circular 
constriction, which pursues the morsel without intermis- 
