THE ANTHOZOA 



51 



teries are formed only in the sulco-lateral exocoeles. They are 

 formed in couples, each couple comprising a macromesentery and a 

 micromesentery, in such wise that the former is always nearest 

 the sidcar directives. The resulting arrangement is shown in Fig. 

 XXIV. It will be observed that five of the original six pairs of 

 mesenteries are pushed up towards the asulcar surface and there 

 form an asulcar group, characterised by the fact that in the lateral 

 members of the group the macromesenteries are nearest to the 

 amlcar directives. Some members of the Zoanthidea show a slight 

 modification of this arrangement, in that the mesenteries 6, 6, 

 forming couples with 1, 1, are macromesenteries. Such a modified 



MICROTYPE 



MACROTYPE 



4. 



Fig. XXIV. 



Diagram of the final arrangement of 

 the mesenteries in the Zoantheae. Tlie 

 left of the figure shows the microt.vpal, 

 the right the macrotypal arrangement. 

 Numerals as in Fig. XXIII. 3 and 4. 

 The five mesenterial pairs, 1, 1 ; 2, 2 ; 4, 4 ; 

 5, ; 0, 0, occupy the asulcar aspect of the 

 zooid, and it is seen that in this region the 

 macromesenterj- of each couple is furthest 

 from the sulcar directives. In the re- 

 maining sulcar region the macromesentery 

 of each couple is nearest the sulcar direc- 

 tives. 



arrangement is known as the macrotype, the normal arrangement 

 being called the microtype. The difference is made use of for 

 purposes of classification. 



The Ceriantliidea form a limited group, comprising the genera 

 Cerianthus, Bathyanthus, and Saccanthus. Cerianthus is a solitary 

 Zoantharian, living imbedded in the sand. Its basal extremity 

 is rounded, and provided with a terminal pore. The column is 

 elongated, cylindrical, smooth, protected by a non-adherent case 

 formed of a felt-work of nematocysts containing grains of sand 

 and other bodies. The peristome is large, provided with two 

 circlets of tentacles — marginal and labial (Fig. XXV. 1). There 

 is a single ciliated groove in the stomodaeum, which is apparently 

 not the sulcus but the sulculus. The mesenteries are numerous, 

 and all but the very short pair on the side furthest from the 

 ciliated groove are complete. The musculature of the mesenteries 



