$ 387. THE POLYPI. 45 
tacles have only a single row of cilia, which move regularly and volunta- 
rily, like the rotatory organs of the Rotatoria. 
By means of the currents produced by the cilia of their tentacles, many 
Polyps draw towards their mouth light particles of food; others make 
use of their ciliated arms to seize larger portions.© This act is aided Ly 
the nettling and various prehensile organs, which are more usually found — 
upon those Polyp-arms having no cilia. These organs are found upon the 
tentacles of Actinia, Edwardsia, Veretillum and Alcyonium, and without 
doubt serve for the seizing of the prey as well as its retention until death. 
But these should not be confounded with special prehensile organs found 
on the tentacles of certain species. These consist of a small coriaceous 
capsule, from which the animal can project a kind of sting. By means of 
these organs, the animal. can attach itself like a bur to external objects, 
and not by suction, as is generally supposed. 
The circular or oval mouth is always situated in the centre of the an- 
terior extremity of the body; it is often surrounded by a lip formed of 
circular fibres.~ In a few species, the mouth projects like a cone at the 
base of the tentacles.“? With the Plwmatellae™ the mouth is topped by a 
tonguelet covered with rapidly moving cilia. Some of the Anthozoa, 
which capture animals of considerable size, can, in swallowing them, dilate 
their mouth to an astonishing width.“ 
DIGESTIVE CAVITY OF ANTHOZOA. 
§ 37. 
The simple stomach of Anthozoa, which is of a variable length, opens 
‘in general directly external by means of the mouth,” and with a few 
species, only, is there a muscular oesophagus. 
With some, the stomach blends with the walls of the body,™ but usually 
it is more or less isolated. There remains, therefore, a cavity of the body 
of variable size, and which is directly continuous with the cavities of the 
arms. In those Polyps living in colonies, it is prolonged into canals trav- 
ersing the corallum, and in this way the cavities of the bodies of all the 
ment is still unprojected (see his Memoir in the 
7 Flustra, Eschara, Tubulipora and Crista- 
tella. 
8 Actinina, 
9 Hydra, Coryne, Eleutheria, Sertularia, Cam- 
panularia and Alcyoni 
10 Such prehensile organs have been observed by 
Quatrefages upon the clavate tentacles of Eleu- 
theria. He thinks also he has observed two mus- 
cles in their capsules, by which the retractile sting 
is projected (Ann. d. Sc. Nat. XVIIL. 1842, p. 276 
and 283, pl. VIII.; or Froriep’s neue Notizen, 
1848, No. 543, p. 230). The oval vesicles which 
roughen the les of Camp aria, and which 
Loven (Wiegmann’s Arch. 1837, I. p. 252) has de- 
scribed as small spinous warts, are probably of the 
same nature. In Hydra each hook-organ upon the 
arm is surrounded by a group of similar vesicles, in 
the interior of which is a rigid bristle.- These or- 
gans are here found orly upon the arms. They 
are distinguished from the organs having hooks by 
their less size, and from their having no project- 
ing filament. Corda has not properly distin- 
guished them from the hook-organs, whose fila- 
Nov. Act. physico-medica XVIII. p. 300, Tab XV- 
fig. 5, 9, 10). Perhaps the organs which Erd? 
(Miller's Arch. 1841, p. 424, Taf. XV. fig. 3) has 
seen upon the tactile lobules of Veretillum cyno- 
morium are of this kind. 
ll Actinia and Edwardsia. 
12 Hydra, Coryne and Campanularia- 
13 Aleyonella and Cristatedla. 
l4 Actinia and Hydra. 
1 Veretillum, Alcyonium, Actinia and Hydra. 
2 Edwardsia. See Quatrefages (Ann. d. Se. Nat. 
XVIIL. pl. I. fig. 2; pl. IL. fig. 1,2) 
3 Hydra. The stomach of the arm-polyps is not, 
as has been formerly supposed, a simple excavation 
in the body. It has proper walls distinct from 
those of the body, by which, however, they are 
closely embraced. There is, therefore, in Hydra 
no cavity of the body, and the cavities of the ten- 
tacles open directly into the stomach. This is also 
true of E/eutheria (Quatrefages, Ann. d. Sc. Nat. 
XVIII. p. 283). 
