The porifera and coelentera . ggests that theZoanthidea have branched off from a parent form common to theIvlwardsiidea and themselves, and are not descended from anEdwardsia form, as are the groui)s hitherto considered. Be thisas it may, the subsequent development is i)eculiar. New mesen- THE ANTHOZOA 51 teries are formed only in the sulco-lateral exocoeles. They areformed in couples, each couple comprising a macromesentery and amicromesentery, in such wise that the former is always nearestthe sidcar directives. The resulting arrangement is shown in It will be observed that five of
The porifera and coelentera . ggests that theZoanthidea have branched off from a parent form common to theIvlwardsiidea and themselves, and are not descended from anEdwardsia form, as are the groui)s hitherto considered. Be thisas it may, the subsequent development is i)eculiar. New mesen- THE ANTHOZOA 51 teries are formed only in the sulco-lateral exocoeles. They areformed in couples, each couple comprising a macromesentery and amicromesentery, in such wise that the former is always nearestthe sidcar directives. The resulting arrangement is shown in It will be observed that five of the original six pairs ofmesenteries are pushed up towards the asulcar surface and thereform an asulcar group, characterised by the fact that in the lateralmembers of the group the macromesenteries are nearest to theamlcar directives. Some members of the Zoanthidea show a slightmodification of this arrangement, in that the mesenteries 6, 6,forming couples with 1, 1, are macromesenteries. Such a modified MICROTYPE MACROTYPE Fig. XXIV. Diagram of the final arrangement ofthe mesenteries in the Zoantheae. Tlieleft of the figure shows the ,the right the macrotypal as in Fig. XXIII. 3 and five mesenterial pairs, 1,1; 2, 2 ; 4, 4 ;5, 0 ; 0, 0, occupy the asulcar aspect of thezooid, and it is seen that in this region themacromesenterj- of each couple is furthestfrom the sulcar directives. In the re-maining sulcar region the macromesenteryof each couple is nearest the sulcar direc-tives. arrangement is known as the macrotype, the normal arrangementbeing called the microtype. The difference is made use of forpurposes of classification. The Ceriantliidea form a limited group, comprising the generaCerianthus, Bathyanthus, and Saccanthus. Cerianthus is a solitaryZoantharian, living imbedded in the sand. Its basal extremityis rounded, and provided with a terminal pore. The column iselongated, cylindrical, smooth, protected by a non-adherent caseforme
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