144 



Dr. J, E. Duerden on the 



represent only a part of a third cycle. A section of a polyp 

 of Cladocora, with sixteen pairs of mesenteries, is represented 

 diagram matically in fig. 2 a. 



Fig. 2. 



Diagrammatic representation of tlie mesenterial arrangement in four 

 dirt'erent polyps of Cladocora arbuscula (Les.). a, as found in most 

 mature polyps of a colony ; b-d, as met with in three enlarged 

 polyps. Inthe enlarged polyps, many pairs of mesenteries have been 

 added to the lirst and second cycles, including an additional pair 

 of directives (D), but no new cycles or orders of mesenteries are 

 formed. 



Colonies of C. arhuscula are sometimes found bearing one 

 or more polyps in which the tentacles, mesenteries, and septa 

 greatly exceed the numbers just given ; wliile now and again 

 an enlarged polyp occurs with two oriil apertures on a single 

 disk, surrounded by a single system of tentacles. 



The mesenterial plan of three of the enlarged polyps is 

 diagrammatically represented in fig. 2 {b-d). In all three 

 polyps, the usual hexameral plan of the mesenteries is alto- 

 gether departed from. Iiregular numbers of mesenterial 



