POLYPIFERA. 



On observing these zoophytes in the living 

 state, each polype is seen to be capable of 

 executing individual movements t sometimes 

 they expand their tentacles, or bend them in- 

 wards towards their mouth, or retract them 

 into the interior of their bodies, or retreat en- 

 tirely into the substance of the common poly- 

 pary, as into a cell, without the neighbouring 

 polypes at all changing their position. In this 

 respect each polype is independent of the sur- 

 rounding ones. Under other circumstances, 

 however, this is not the case, for sometimes 

 the common body of the creature evinces 

 movements that influence all the polypes, and 

 cause their simultaneous contraction ; and this 

 contraction is occasionally continued to such 

 a degree that all the soft upper portion shrinks 

 into the coriaceous stem, so as to become im- 

 perceptible, as represented in the figure (fig. 

 30, e). On separating one of the polypes 



Fig. 31. 



Alcyonldium, elegans. Upper portion of one of the 

 polypes magnified, and opened longitudinally. 



a, tentacles; b, mouth; c, stomach; d, inferior 

 aperture of the stomach ; e, upper part of the ab- 

 dominal cavity ; f, membranous partitions extend- 

 ing from the stomach to the walls of the cavity in 

 which it is suspended (some of these are cut in the 

 section, others are in place) ; f, longitudinal folds 

 of the abdominal parietes continuous with these 

 partitions ; g, the canals that surround the stomach 

 and terminate in the tentacles : gf, one of the ten- 

 tacles laid open ; h, groups of spicules situated at 

 the base of the tentacles ; k, filiform appendages to 

 the stomach, probably hepatic. (After Milne Ed- 

 wards.} 



from the common mass, and opening it under 

 a microscope in a longitudinal direction, it is 

 found that its central portion is occupied by 

 a cylindrical stomach (fig. 31, c) which is 

 open at both extremities, and presents in- 

 ternally eight longitudinal bands and a multi- 

 tude of transverse folds : inferiorly it is con- 

 tracted, and looks as if its termination was 

 surrounded by a sphincter, although no mus- 

 cular fibres are perceptible. At length the 

 inferior contracted orifice of the stomach opens 



into a wide cavity (d), which occupies the en- 

 tire diameter of the polype, and is prolonged 

 inferiorly into the substance of the polypary. 

 The calibre of the stomach itself is much 

 smaller than that of the body of the animal, in 

 the centre of which it is suspended by means 

 of eight membranous and extremely delicate 

 septa (/), which pass between the outer sur- 

 face of the stomach and the parietes of the 

 polype, forming so many vertical partitions. 

 By their upper extremity these septa are 

 blended with the periphery of the mouth, and 

 thus circumscribe between them eight longi- 

 tudinal canals (g), which are continuous with 

 the corresponding tentacles. These latter ap- 

 pendages are in fact entirely hollow, and pre- 

 sent on each side of the cavity which they 

 enclose a series of ten or a dozen little aper- 

 tures opening into the pinnules along their 

 borders. 



Inferiorly, the eight interseptal compart- 

 ments communicate freely with the great ca- 

 vity (d), situated beneath the stomach, the 

 membranous septa becoming gradually conti- 

 nuous, with eight longitudinal folds (/') that 

 project into its interior. Just at the point 

 where each of the membranous septa ceases 

 to be continuous with the walls of the sto- 

 mach and becomes free by its inner margin, 

 may be observed a filiform flexuous organ (k\ 

 the nature of which appears to be glandular. 



The common polypary from which these 

 polypes issue is composed, as was stated 

 above, of two distinct portions (fig. 30, b, c), 

 The superior soft portion is found by dis- 

 section to be made up of an assemblage of 

 longitudinal membranous tubes placed parallel 

 to each other, and so closely conjoined that 

 it is difficult to separate them, and in fact 

 the hard base of the polypary is nothing more 

 than a continuation of these tubes, slightly 

 altered in their structure : those situated 

 near the centre of the stem are only distin- 

 guishable by a slight thickening of their walls, 

 but those near its circumference acquire a 

 much harder consistence, their parietes being 

 encrusted with multitudes of brown-coloured 

 fusiform spicula, which appear to be composed 

 of a cartilaginous substance and of carbonate 

 of lime. These spicula are arranged in a 

 longitudinal direction, and confer upon this 

 part of the polypary its solidity and peculiar 

 aspect. Near the circumference of the poly- 

 pary many of the tubes seem to be obliterated 

 by pressure of the contiguous parts. On 

 tracing the tubular structure downwards 

 towards the base, each tube gradually disap- 

 pears, either by becoming obliterated, or by 

 anastomosing with the surrounding ones, 

 whilst superiorly it is found to be continuous 

 with the abdominal parietes of a polype, the 

 sheath of which it forms when it is in a state 

 of contraction. 



The tubes thus united into fasciculi are 

 evidently analogous to the cavities into which 

 the polypes of Alcyons, Corals, &c., withdraw. 

 These cavities are generally called "pohpi- 

 ferous cells," and some writers consider them 

 as being species of cases or envelopes more 



