140 
ZOOLOGY, 
The mouth is situated on a disk (Jophophore, Fig. 9%, B), 
bearing the tentacles, which are hollow processes of the 
body-walls, communicating with the body-cavity, the blood 
flowing into them, there being aérated, while they are exter- 
nally ciliated. They serve both to catch food and for respir- 
ation as makeshift gills. Hyatt states that the tentacles are 
used not only to catch the prey, but for a multitude of other 
offices. They are each capable of in- 
dependent motion, and may be twisted 
or turned in any direction ; bending 
inwards, they take up and discard 
objectionable matter, or push down 
into the stomach and clear the 
cesophagus of food too small to be 
acted upon by the parietal muscles. 
They are also employed offensively in 
striking an intrusive neighbor, and 
their tactile power, sensitive to the 
H (ail slightest unusual vibration in the 
Fig. 97.—Organization of a 
Polyzoon. A, Paludicella 
Ehrenbergii. B, Plumatella 
Sruticosa. br,tentacular bran- 
chiz of lophophore; ce, ceso- 
phagus; v, stomach: r, intes- 
tine; a, anus; 7, cell; a, pos- 
terior, z!, anterior, cord, at 
the insertion of which into 
the body the generative prod- 
ucts are developed; t, testes; 
oO, ovary; m, retractor mus- 
cles of the anterior portion of 
the cell; mz, priucipal retrac- 
jtee muscle.—After Allman. 
water, warns the polypide of the ap- 
proach of danger. 
The digestive canal hangs free in 
the body-cavity, only attached by the 
mouth and anus to the walls of the 
body. It consists of a pharynx, a 
large stomach, and an intestine which 
lies by the side of the pharynx, since 
the canal has a simple deep dorsal 
flexure, the vent being situated on 
the dorsal or cardiac side, near the 
mouth. Usually the stomach is tied 
by a sort of ligament (funiculws) to 
a point on the body-walls, near the 
mouth, The nervous system is rep- 
resented by a double ganglion form- 
ing a single mass situated between the mouth and vent; it 
is highly contractile and changeable in form. ‘There is no 
heart and no circulatory apparatus. The sexes are united 
in a single polypide, the glands forming masses growing on 
