188 



ZOOLOGY 



SECT. 



FIG. 137. Cirripathes anguina, 



portion of colony. (After Broun.) 



pushing* of the disc. In Edwardsia, however, they may be 

 reduced to sixteen, and in some genera of Sea-anemones they are 

 branched. In the Antipatharia (Fig. 137) they vary in number 



from six to twenty-four. In the 



t/ 



Alcyonaria on the other hand, the 

 tentacles, like the mesenteries, are 

 eight in number and are always 

 pinnate, i.e. slightly flattened and 

 with a row of small branchlets 

 along each edge (Fig. 131). Many 

 Actiniaria have the tentacles per- 

 forated at the tip (Fig. 125, A, >.), 

 and in some species these organs 

 undergo degeneration, being re- 

 duced to apertures on the disc, 

 which represent the terminal 

 pores of the vanished tentacles, 

 and are called stomidia. 



Many Sea-anemones possess 

 curious organs of offence called 

 acontia (Fig. 125, A, and Fig. 144, 



ac.). These are long delicate threads springing from the edges 

 of the mesenteries : they are loaded with nematocysts, and can 

 be protruded through minute apertures in the column, called 

 ' port-holes " or cindidcs (en.). 



Enteric System, The gullet in the Actiniaria presents some 

 remarkable modifications. It is usually a compressed tube with 

 two siphonoglyphes, but in Zoanthus and some other genera the 

 ventral gullet-groove alone is present (Fig. 130, B), and in Gyractis 

 both grooves are absent, and the tube itself is cylindrical with a 

 circular mouth. The ordinary compressed form of gullet often 

 assumes, in the position of rest, a x-shaped transverse section, 

 owing to its walls coming together in the middle and leaving the 

 two ends wide open. In a deep-sea form, Halcampoides, there is a 

 longitudinal partition dividing the stomodaeum into dorsal and 

 ventral tubes, the latter of which is said to serve for the egestion 

 of waste matters, and so act as an intestine. In some forms the 

 bluntly-pointed proximal or aboral end of the body is perforated by 

 a small aperture which seems to serve as an anus. In two recently 

 described genera, Fc-nja (Fig. 138) and ^Kyir, a very remarkable 

 modification is described : the gullet is continued to the aboral 

 end, when it opens on the exterior by an anus (a.), thus forming 

 a complete digestive tube. By this arrangement the inter- 

 mesenteric chambers are shut off from all communication with the 

 digestive tube, and together constitute a cavity surrounding the 

 latter and reminding us of the body-cavity met with in most of 

 the higher animals. In Fenja each inter-mesenteric chamber 



