THE ANATOMY OP THE M ADREPORARIA. 3 



mesoglcea, 1 and endoderm, exactly as has been described in 

 Stylophora (7), 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 Dendrophyllia (5), and Rhodopsarnmia (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 con- 

 traction produced by preservation in alcohol has forced the 

 body wall so tightly upon the echiuulations that they project 

 in many cases through it. Again, in Heteropsammia mul- 

 tilobata, a form as closely allied to Rhodopsarnmia as one 

 with ccenenchyme 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 Sty- 

 lophora, 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 contempo- 

 raneously with the development of ccenenchyme, 

 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 ccenenchyme). In other 

 words, the mesenteries 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. 

 Rhodopsarnmia), they could not extend over the ccenenchyme 

 of a form with fused or sunken calicles (e. g. Heteropsammia 



1 The substitution of this word for the misleading " mesoderm " we owe to 

 Bourne (1). 



