OF POLYPES. 41 



portion distended to a bulk which may be more than double of 

 that which it had 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 

 all 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 lamellse 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 Blaitiville, Man. d'Aftinologie, p. 68. 



