sociality in the madreporaria 
245 
as to the mode of asexual reproduction. Howeverj in the study 
of hard parts there appears to be a series in increasing complexity, 
within the family Fungidae, exemplified by the genus Fungia, 
which is invariably solitary ; and Herpetolitha, which has an axial 
series of calices with several peripheral parallel series of calices, 
the septocostae being' continuous between calice and calice ; and 
Polyphyllia, the last step in the series, having calices decreased in 
size, increased in number, and crowded together. 
The genera of the Agariciidae are typically compound, but in the 
Tertiary simple forms appear to have been fairly common (Micro- 
seris, Trochoseris, Palaeoseris, etc.). Cyathoseris, from the OH- 
gocene and Eocene, forms a massive colony by costal gemmation, 
the young corallites remaining permanently in a circle about the 
periphery of the mother polyp. Within the family Agariciidae it 
is possible to choose a graded series of genera and species from 
such forms as Siderastraea, in which a definite pericalicular wall 
interrupts communication between polyps, to certain species of 
Agaricia in which there is no definite pericalicular boundary, the 
septocoste and some of the mesenteries being continuous from 
polyp to polyp. The highest degree of sociality in the Fungida 
appears to be found in Pachyseris, in which the calices are dis- 
posed in parallel rows with continuous and parallel septocostae, 
with continuous columella, and showing no impression in.fhe hard 
parts of distinct calices. 
The most successful corals at the present time are undoubtedly 
those which have the most intimate union between the individual 
polyps; for example, Porites and Acropora in the Perforata, 
meandrine forms in the Imperforata, and in the Fungida those 
corals which have lost definite pericalicular boundaries, as for ex- 
ample the family Agariciidae. In modern reefs the world pyer 
these genera are found to be most numerous in individuals and 
often also in species and varieties. The communication between 
the visceral cavities of polyps in the Perforata is accomplished 
by perforations in the boundary walls, while in the Imperforata 
and the imperforate Fungida a similar result is brought about 
by the abolishment of the walls themselves in the line of con- 
fluence. In the one case the communication is intraskeletal ; in 
the other, supraskeletal. 
The unity and compactness of colonies of the Hexacoralla 
cannot be paralleled among the Tetracoralla, although! the Tet- 
racoralla shows some progress, from the diffuse Diphyphyllum to 
the compact Strombodes or Accrvularia. Modern species have 
