IV 



PHYLUM CCELENTERATA 



157 



canals in immediate connection with the gastropores are traversed 

 by horizontal partitions, the tdbulce (fb). 



In the living animal each pore is the place of origin of a zooid : 

 from the gastropores protrude polypes (Fig. 117, P) with hypostome 

 and four knobbed tentacles ; from the dactylopores long, filamentous, 

 mouthless dactylozooids or feelers (D.Z\ with irregularly disposed 

 tentacles : the function of these latter is probably protective and 

 tactile, like that of the guard-polypes of Plumularia and the 

 dactylozooids of Hydractinia. The bases of the zooids are con- 

 nected with a system of delicate tubes, which ramify through the 



FIG. 116. AXillepora alcicornis. A, part of skeleton, natural size ; B, portion of surface, 

 magnified ; C, vertical section, magnified ; d.p. dactylopores ; g.p. gastropores ; tb. tabulae. 

 (After Nicholson and Lydekker.) 



canals of the coral and represent a much-branched ccenosarc, 

 recalling that of Hydractinia (p. 144). 



The ccenosarcal tubes have the usual structure, consisting of 

 ectoderm and endoderni with an intervening mesoglcea. From 

 the relative position of the parts it will be obvious that the cal- 

 careous skeleton is in contact throughout with the ectoderm of the 

 colony : it is, in fact, like the horny perisarc of the Leptolinse, a 

 cuticular product of the ectoderm. 



The only other genus to which we shall refer is Stylaster (Fig. 

 118), which forms a remarkably elegant tree-like colony, abund- 

 antly branched in one plane, and of a deep pink colour. On the 

 branches are little cup-like projections with radiating processes 

 passing from the wall of the cup towards the centre, and thus 



