IV 



PHYLUM CCELENTERATA 



203 



the Mushroom-coral (Fungia) the corallite is discoid, the theca is 

 confined to the lower surface, and small calcareous rods, the 

 synapticula, connect the septa with one another. 



In the living condition the polype fills the whole interior of the 

 corallite and projects beyond its edge to a greater or less degree 

 according to its state of expansion (C). The proximal part of the 



scfi- 



sefi ff 



se/> 



FlQ. 156. A, B, two views of Flabellum curvatum. C, semi-diagrammatic view of a simple 

 coral ; D, portion of a corallite ; E, F. diagram of a simple coral in longitudinal and trans- 

 verse section ; ectoderm dotted, endoderm striated, skeleton black, b. pi. basal plate ; col. 

 columella ; e. th. epitheca ; gul. gullet ; mes, mes. 1, mes. 2, mesenteries ; mes.f. mesenteric 

 filaments ; sep. septa ; t. tentacle ; th. theca. (A and B after Moseley ; C and D after 

 Gilbert Bourne.) 



body-wall is thus in contact with the theca, which has the relation 

 of a cuticle, and is, in fact, a product of the ectoderm. The free 

 portion of the body-wall is frequently, in the extended state, folded 

 down over the edge of the theca so as to cover its distal portion. 

 The septa alternate with the mesenteries, each lying in the space 

 between the two mesenteries of one couple, and each being invested 



