THE ANATOMY OP THE MADREPORARIA. 415 



nary three layers. The tentacles are apparently both ecto- 

 coelic and entoccelic, and are simple evaginations tipped each 

 by a single battery of nematocysts, as in Seriatopora ("Anat. 

 Madr./' iii, fig. 11). "The septa lie each between a pair of 

 normal mesenteries. No differentiation of particular mesen- 

 teries is recognisable, and all extend to about the same depth 

 into the polyp cavity. The two pairs of directive mesenteries 

 are well marked, but it is worthy of note that the plane in 

 which they lie does not always coincide with the axial-abaxial 

 (dorso-ventral) plane which generally governs the orientation 

 of similar colonies, but is here, in the case of some polyps, at 

 right angles to it. 



Madracis is of especial value as affording an intermediate 

 condition between the two Madreporarian types mentioned 

 above, in that the body wall is supported on the echinulations 

 of the ccenenchyme only in certain more or less limited arese 

 between the polyps, whereas immediately round the calyces are 

 recognisable such peripheral lamella? as are usually charac- 

 teristic of forms devoid of ccenenchyme (fig. 1, b). This is 

 probably due to the fact that the polyp calyces are slightly 

 exsert above the general surface of the colony. 



Here, therefore, we apparently have a condition morpho- 

 logically intermediate between that of a solitary imperforate 

 coral, as, for example, Caryophyllia, and such a cceuenchyma- 

 tous form as Seriatopora. The condition in Caryophyllia 

 (von Koch, ' Morph. Jahrb./ v, fig. 4) and other simple forms 

 is probably the more primitive. The next stage in the series 

 seems to be indicated by the existing condition of Lophohelia 

 prolifera (" Anat. Madrep.," iii, fig. 6), where the polyps and 

 calyces are free and independent of each other, although a 

 colony is formed by gemmation. Next it would appear that, 

 as ccenenchyme was developed (presumably in order to increase 

 the solidity and mass of the colony), and the spaces between the 

 various polyps of the colony filled gradually with coral from 

 below upwards, the peripheral lamella?, as being necessarily 

 confined to the immediate neighbourhood of the calyces, would 

 be inadequate to bridge over the intercalated area? of cceneu- 



VOL. XXVIII, PART 3. NEW SEE. F F 



