OF POLYPES. 
41 
portion distended to a bulk which may be more than double of 
that which it bad previous to the introduction of the fluid, and 
which it resumes when, from the application of irritants, the 
polypes contract themselves, and by their contractions force out 
ail the imbibed water. — The tortuous filaments suspended from 
the base of the stomach have been generally taken for ovaries, 
but the observations of Dr Grant and M. Edwards seem to 
have disproved this opinion. The latter of these eminent na- 
turalists believes them to be analogous to the biliary canals of 
insects. * 
The affinity in structure between the asteroid zoophytes and 
those which we name helianthoid , from their resemblance to some 
compound flowers, is evident, although in the latter there is a 
still further recession from the simplicity of polype anatomy. 
We find in them a mucous coat covering the surface, — beneath 
it a layer of transverse submuscular fibres, while the body is sup- 
ported by numerous strong cartilaginous lamellae arranged in 
longitudinal parallelism. Each of the lamellae is attached in- 
feriorly to the circular layer which constitutes the base of the 
animal, and divides into three fascicles, — one which goes to the 
stomach and to the rim of the oral aperture, — another to the 
roots of the tentacula, — and the third is prolonged to the outer 
labial border, where it is bent back to form its free margin, -f- 
The stomach has its distinct and proper parietes ; there are 
special organs for the developement of the reproductive gemmae ; 
and even some traces, as is asserted, of a nervous system ; while 
the numerous tentacula are perforated like canals, in order that 
the water of respiration may be introduced into the interior, and 
the nutritive fluids more thoroughly influenced by its oxygen. 
It has been mentioned already that there is no proper circu- 
lation — no movement of a fluid analogous to blood in appropri- 
ate vessels — in any zoophyte, but in many of the hydroida it 
has been discovered that there is a continuous and uniform cur- 
rent of a fluid, containing granular bodies which have them- 
selves a rotatory motion, within the tubular portions of the horny 
polypidom. Cavolini first detected this sort of circulation, which 
* Ann. des Sc. Nat. iv. 331 ; an. 1835. 
f Blainvilie, Man. d’Actinologie, p. 68. 
