POLYPS. 71 
Of the nervous system of Polyps little is known; it has not 
been described as a connected whole, but different observers have 
imagined that they had discovered ganglia or a nervous ring near 
the mouth. From analogy it is probable that the nervous system, 
where it exists, does form a ring round the mouth; and that the 
threads, which Sp1x described in the pedal disc of Actiniw as 
nerves, can on this account scarcely be considered to be such. As 
organs of sense, four coloured spots at the edge of the disc have 
been observed in the Medusa-form products of Syncoryne and Coryne 
fritillaria of STEENSTRUP, which entirely resemble the parts that 
EHRENBERG considers to be eyes in Medusa. Still more distinct is 
this organ in a form described by QUATREFAGES, which he names 
Lleutheria dichotoma. Here this author found six eyes with a 
hemispherical lens, a granular pigment of a red colour, and a 
spherical projection of the integument closing the eye like a cornea’. 
In ryozoa the muscular system is most largely developed, and 
serves principally to retract the animal within its cell. It protrudes 
itself partly by straightening the alimentary canal, partly by means 
of transverse muscular fibres which contract the diameter of the 
visceral cavity, and in that way elongate it?. Traces of a muscular 
system have also been met with in other Polyps. 
As to the geographic distribution of Polyps, we have only 
imperfect notices. Fresh-water Polyps, Hydra, Alcyonella, Plu- 
matella, have, as far as I know, only been observed in Europe; but 
from this to conclude that they do not occur in tropical regions, 
would probably be premature. Still KurenBera found no Hydre 
in Africa and Arabia. Actiniw are met with in all seas. The 
Polyps with polyparies, which are almost all inhabitants of the sea, 
are richest in species in warm regions; //lustra, amongst the 
Bryozoa, is it seems an exception to this: the European species of 
this genus are about as numerous as the foreign: these last come 
principally from New Holland; Gorgonia occurs in all seas, but 
Van BENEDEN, MWém. sur les Campanulaires de la céte d’ Ostende, Mém. de V Acad. 
Royale de Brumelles, Xvi. 1843. Ann. des Se, natur., sec. Série. Tom, Xx. Zool. pp. 
35°—373- . 
Dusarvin, Mémoire sur le dévéloppement des Méduses et des Polypes hydraires. Ann. 
des. Sc. Nat. 3¢ Série. Tom. 1v. 1845. Zoologie, pp. 257—281. Pl. xv. xv. 
1 Ann. des Sc. Natur. sec, Série. Tome xvitt. p. 280. Pl. vin. fig. 6. 
2 Minutely detailed by Farre in Bowerbankia, Phil. Transact. 1837. pp. 393—399- 
