ANTHOZOA ZOANTHARIA. 735 



primary, e.g. in Sagartidae and Liponemidae^- . The Amphianthidae live 

 attached to fragments of the stems of Axifera, and like Gerardia (infra, 

 p. 737) have the sagittal or antero-posterior axis short, and the transverse 

 elongated. In Halcampa the aboral end of the body is rounded, and it is 

 pierced by numerous (24 ?) small openings. Its mesenteries are reduced 

 to the primary six pairs 2 . The Hexactiniae live usually attached to rocks, 

 or when the base is feebly developed, immersed in sand or mud. The 

 Minyadinae, which probably belong to this tribe, are pelagic. The base 

 may be inverted and serve as an air vesicle, but in Nautactis is capable 

 of eversion and attachment. It is perforated in Dactylominyas (Oceanactis) 

 rhododactyla. 



(2) The Paractiniae of Hertwig differ from the Hexactiniae in having 

 the mesenteries multiples of 8 ; Sicyonis has 64 : but Polyopis 36, there 

 being in Hertwig's opinion two redundant pairs in this case. Polyopis has 

 the tentacles reduced to stomidia, and has a rounded aboral pole. 



(3) The Monatdeae, represented by Scytophorns striatns, have seven 

 pairs of complete mesenteries, one only of which is directive. The single 

 siphonoglyphe corresponds to it. The animal is hermaphrodite : the testes 

 are situated near to the base, the ovaries at a higher level. 



(4) The Edwardsiae possess eight mesenteries, all complete, all bearing 

 reproductive organs. There are two pairs of directive mesenteries ; the 

 remainder are not paired and have the retractor muscles turned in the 

 direction of one of the two pairs of directive mesenteries, hence termed 

 ventral. There are two siphonoglyphes. The arrangement is therefore 

 neither Alcyonarian nor Hexactinian. The tentacles vary in number with 

 age (12-36), and are more numerous than the mesenteries, a fact which 

 probably denotes the loss of mesenteries by reduction. The body is divisible 

 into three regions ; the middle one ( = scapus) is covered by a tough 

 mucoid investment ; the posterior is pointed but not perforated. The 

 animals live immersed in sand or mud, in holes of rocks or under the roots 

 of seaweeds. 



(5) The Zoanthidae have the mesenteries paired as in the Hexactiniae, 

 but each pair consists typically of a complete mesentery, the macro-septum, 

 which has a mesenterial filament, and bears genital organs, and of an in- 

 complete mesentery, the micro-septum devoid of both the structures 

 named. The directive mesenteries are as in Hexactiniae, but one pair con- 



1 In Ophiodiscus the mesenteries of the fourth order are devoid of mesenterial filaments and 

 muscles, and bear the genital organs, the mesenteries of higher orders being muscular and sterile. 

 So too perhaps in Polystomidium. See also note, p. 726. 



2 The base is rounded also in Ilyanlhus, in Siphonactinia ( = Peac/ita) and Philomedusa, but 

 whether perforated or not is uncertain. The mesenteries and retractor muscles of Siphonactinia are 

 apparently restricted in number and peculiarly disposed, its base perforate according to Faurot, 

 C. R. 98, 1884. It must be borne in mind that the present arrangement of the Hexactiniae in families, 

 &c. is not founded throughout on anatomical structures : it can only be regarded as temporary. 



