THE ANATOMY OP THE MADREPOFiARIA. 251 



means of sections are found to consist of dead tissues and algal (1) 

 parasites. There is really no epitheca present, recognisable as such, 

 in the adult. 



The columella (fig. 3, col.) is incomplete, the septa not always 

 meeting regularly along their free edges. 



In the retracted condition of the polyp there is no tissue external 

 to the corallum (figs. 1, 2), nothing corresponding to the condition 

 described by Heider in Cladocora and by v. Koch in Caryophyllia. When 

 expanded, however, the soft tissues almost certainly stretch outwards 

 and downwards over the upper fourth of the exterior of the theca, 

 which is thus kept white and hard, as mentioned above. Were the 

 polyp thus completely expanded to be plunged into a killing fluid, the 

 same appearances would ensue as the above-named observers have 

 described. 



ii. Anatomy. — This agrees in all essential details with the Actinian 

 type, except in the absence of an external body-wall, the whole polyp 

 being enclosed in the corallum (figs. 1, 2). Moseley mentions that in 

 some specimens tissues external to the theca were observed round the 

 lip, and figures them (II), pi. xvi, fig. 10, as consisting of ectoderm 

 and mesoderm, but had not the means of studying them by sections. 

 None of my specimens had any trace of such, and from observations 

 on Desmophyllum, a closely-allied form, I imagine that these tissues 

 were simply due to the expansion of the polyp, and contained a con- 

 tinuation of the coelenteron such as was described by v. Heider in 

 Cladocora. On decalcification the polyp appears conical, and divided 

 into a series of wedges by the spaces where the septa had been. At 

 the base of the polyp — i.e. the apex of the cone — these wedges appear 

 to be connected together by little bridges of tissue. These latter are 

 of no morphological importance, being due apparently merely to the 

 incompleteness of the columella, and their arrangement varies in 

 different specimens. The polyp consists of a mouth-disc bearing 

 tentacles ; a stomatodeeum, which opens into the coelenteron, the latter 

 being periaxially divided into exocceles and entocoeles by the mesen- 

 teries. 



The mouth-disc (fig. 2, md) is peripherally fastened to the extreme 

 edge of the lip of the calyx, and is centrally invaginated into the 

 typical Anthozoan stomatodeeum. 



On the disc are borne the tentacles, which are simple hollow 

 evaginations of the entocoeles — i.e. one is placed over each septum. 



