736 THE ANIMAL KINGDOM. 



sists of two macroscpta, the other of two microsepta. The former is termed 

 ventral and to it corresponds the single siphonoglyphe. The remaining 

 pairs of mesenteries are disposed so as to constitute two zones, a dorsal and 

 a ventral. The former always has, even in the youngest specimens, five 

 pairs of mesenteries, including the directive pair. On each side of the latter 

 there is a pair of the typical Zoanthidan structure, and then a pair, either of 

 the typical structure or composed of two macrosepta. The first-named dis- 

 position is termed the microtype, the second the macrotype. The ventral 

 zone contains a variable number of mesenterial pairs according to age, but 

 all of the typical structure, with the exception of the directive pair. In 

 both the dorsal and ventral zones the mesentery immediately adjoining 

 the directive pair is a macro-septum. New pairs are intercalated only in 

 the interseptal space on either side of the ventral directive pair. The ten- 

 tacles are disposed in two circles ; one set corresponding to the intra-septal 

 chambers, the other to the inter-septal. Rotteken's muscle is well developed 

 and embedded in the mesoglaea except in Palythoa. The mesoglaea is 

 filled with islands or branching cords of cells derived from the ectoderm, 

 and it is traversed by radial nucleated muscle-fibres. It also contains, ex- 

 cept in the genera Zoanthus and Mammilifera, foreign bodies, particles 

 of sand, calcareous fragments, spicules of Sponges, shells of Foraminifera or 

 Radiolaria. The sexes are united in Zoanthus, separate in the colonies of 

 Epizoanthtis and Palythoa : not known in the other colonial genera. The 

 animals are fixed and colonial or free. Of the former, Zoanthus has 

 branched stolons ; Mammilifera stolons with a tendency to form lamellae ; 

 Epizoanthus a lamellate base ; Palythoa a band-like base, whilst in Corti- 

 cifera the zooids are imbedded in a coenosarc. The stolons, lamellae, or 

 coenosarc are traversed by a system of canals which communicate with the 

 gastric cavities of the zooids at their bases. The colonies are fixed to 

 stones except in the genus Epizoanthus, which grows either upon empty 

 shells of Mollusca, on the rooting spicules of Hyalonema, or on a shell in- 

 habited by a Hermit Crab, and then the substance of the shell is resorbed 

 by the coenosarc. The free-living Zoanthidae comprise the genus Sphe- 

 nopus, in which the body is drawn out into a hollow peduncle terminating 

 in a disc sunk in sand, &c., and an unnamed dioecious genus with buds 

 originating from the base of the peduncle. 



(6) The Cereantheae have numerous complete mesenteries, not disposed 

 in pairs nor multiples of 6. There is a single siphonoglyphe which deter- 

 mines a ventral aspect. Two median mesenteries, which correspond to 

 this siphonoglyphe are minute, and from their position are termed directive. 

 The mesentery on either side of these two is of very great length and 

 reaches to the aboral pole. The remaining mesenteries diminish in size to 

 the middle dorsal line, the spot where new mesenteries are added. There 

 are no retractor muscles, but each surface of a mesentery has feebly 



