THE ANATOMY OF THE MADREPORARIA. 19 



Madrepora (3), &c. ; its continuity is only broken by the mouth 

 orifices of the polyps. 



What the exact relation of this body wall to the tissues actually 

 apposed to the theca may be, i.e., whether it agrees with the 

 undoubted relations described in Astroides embryo (8), in Dendro- 

 phyllia (5), and Ehodopsammia (2), or with the apparently equally 

 accurate relations recorded for Stylophora (7) and Madrepora (3), 

 is exceedingly difficult to determine. In my specimens, both of 

 Madrepora and Turbinaria, the contraction produced by preser- 

 vation in alcohol has forced the body wall so tightly upon the 

 echinulations that they project in many cases through it. Again, 

 in Heteropsammia multilobata, a form as closely allied to Ehodop- 

 sammia as one with coenenchyme can be to one devoid of it, the 

 relations appear to be identical with those in Madrepora and 

 Stylophora, and such as I have here (Fig. 2) drawn for Turbinaria. 

 If we are justified in crediting the appearance of the tissues in 

 Stylophora, Madrepora, and Turbinaria, which implies that the 

 body wall is supported upon the echinulations (Fig. 2), it is not 

 perhaps too much to infer that these relations are of secondary 

 significance, and have arisen contemporaneously with the development of 

 coenenchyme, for the support of the external body wall, owing to the 

 inadequacy of ^the peripheral sections of the mesenteries to effect 

 this support elsewhere than immediately round the theca (where 

 this is exsert from the coenenchyme). In other words, the mesen- 

 teries are necessarily confined to the polyp cavity, and their 

 peripheral sections to the small part of it which is cut off (?) from 

 the rest by the upward growth of the theca ; while therefore they 

 are amply sufficient for the support of the body wall in a form with 

 separate free calicles (e.g., Ehodopsammia), they could not extend 

 over the comenchyme of a form with fused or sunken calicles (e.g., 

 Heteropsammia multilobata), which is, by its very nature, outside of, 

 and in a manner independent of, the polyp cavities. 



Of the more primitive (?) condition, Astroides embryo (8), Ehodop- 

 sammia (2), Dcndrophyllia (5), and Fungia (1) stand as admitted 

 examples among the Perforata ; Cladocora (4), and Caryophyllia (6) 

 among the Im perforata, all being forms with free calyces ; while of 

 the secondary condition, Madreponi (4), Heteropsammia multilobata 

 (which I hope to describe in a future memoir), Turbinaria among 



