132 



The tentacles, or the pores of the retracted tentacles, form a 

 circlet half-way between the epitheca and the stomodoeum, 

 and the peristome is irregularly contracted into ridges 

 between the attachments of the mesenteries. The stomo- 

 doeum may be either extremely reduced or enormously 

 enlarged, the former if the polyp has been slowly killed in 

 spirit or chromic acid, the latter if more rapidly fixed in 

 formalin. To a certain extent the appearance and size of 

 the stomodoeum depends on the state of retraction of the 

 tentacles, being much larger when the latter are but partially 

 invaginated. 



Fig. I. Partly diagrammatical transverse section through a sixiiile completely 

 retracted specimen of 7*'. rubrum indifferent planes: — A. Through the top of the 

 epitheca a little below its edge: B. Through the stomodoeum, cutting the basal 

 contracted ends of some of ihc tentacles: C. Through the top if thi masEes of 

 gtnerative organs : D. Through the bottom part of the generative organs. 



The numerals refer to the cycles of the septa, f. Tentacles, -st. JSfeomodoeuiii. 

 p.w. Peristome wall. »i.f. Mesenterial fllameuts. </ Testicular masses. 



Tlie sections were slightly simplified from camera iucida drawings. In addi- 

 tion to the general anatomy they show the decrease in size at d disappearance of the 

 mesenteries and septa lower down in the corallite. One of the mesenteries of a 

 pair bounding a septum of cycle 4 reaches the stomodi eum (see B) and is so repre- 

 sented, although it is very unususl for such an one to do so. 



Septa and Mesenteries.— When decalcified, the polyp is 

 divided up into as many chief segments as there are larger 

 septa. These are joined over the open mouth of the calicle by 



