12 Coelenterata. 



* 



is marked off from the regenerated portion by large grooves, a complete union 

 of the two pieces giving rise to a Cycloseris, a Diaseris not being met with 

 in patella. Autotomy is also met with in distorta, probably also in cyclolites 

 and oahemsis, there being also a tendency in this direction in Danai. In other 

 species there is a lappetting of the border (Scutaria-grou^), the last trace of the 

 autotomy which is so prominent in the most primitive species. 



Pace( I ) refutes the view that the parent polyp of a Turbinaria colony dies 

 away and its calicle becomes submerged in the coenenchym and that therefore 

 the cup is produced by fusion of the walls of daughter-polyps only. In veiy 

 young stages the parent polyp does not die away but bends over to one side 

 and takes part along with its daughter-polyps in forming the rim of the cup. 

 The parent calicle can always be traced in a normal cup as one, generally 

 the largest, of the innermost ring of calicles. The variations in form of a 

 colony can be readily explained by reference to the conditions under which 

 the coral has grown. The most perfect cups are found in clear water below 

 the tidal zone, where their growth is unrestricted by neighbouring objects. 

 Above extreme low water mark there is a tendency for the coral to become 

 irregular by folding of its walls and by adoption of an encrusting habit. Spe- 

 cimens are common on the reefs in which some calicles have budded to form 

 secondary more or less independent colonies : subsidiary cups may thus be 

 formed within the parent cup. When the coral is growing at the bottom of 

 a hole in the reef, where growth in a vertical direction is of obvious advan- 

 tage to the colony, the secondary colonies assume an arborescent form re- 

 sembling a Madrepore (T. maxima, Ortmann). When on a shelf of rock, the 

 side of the T. turned away from the free edge of the shelf ceases to grow 

 and the corallum thus becomes a flattened plate overhanging the ledge (reni- 

 formis and foliosa, Bernard?). If during growth the lower surface of a cup 

 come into contact with the substratum irregular root-like outgrowths arise at 

 the points of contact (radicalis, Bernard). The form of the corallum is fre- 

 quently modified to adapt it to life on muddy ground, the cup becomes flat- 

 tened out (the "peltate" ' type of Bernard) or may even become convex, or else 

 the cup may be cleft on one side or perforated at its base so as to render 

 it impossible for any silt to lodge within it, or at an early stage the margin 

 of the cup, or rather disc, becomes frilled thus producing a series of radial 

 gutters. By modifications during further growth a corallum may be formed 

 consisting of numerous close-set vertical plates (gracilis, Bernard) or of a series 

 of radiating cups or cylinders connected at their bases. The author finds 

 (with Bernard) that the tabulate type is expressive of periodicity of growth 

 apparently dependent upon the monsoons which affect the "set" of the currents. 

 The glomerate type in which the corallum formes a large hemispherical mass 

 appears to be an adaptation to withstand the battering of the surf and the 

 rush of the tide. Many of the features for the discrimination of species thus 

 prove to be of secondary value, but there are distinct species of T. since spe- 

 cimens growing side by side and consequently under the same conditions may 

 still exhibit quite obvious differences of type. 



Pace( 2 ) has collected in Torres Straits specimens of Lithophyllia from 3 or 

 4 to 20 fathoms. The shape is very variable, but directly dependent on- the 

 environment: where the bottom is hard and free from mud the calyx is deep, 

 but where, as for example at the place from which the "Challenger" obtained 

 the type specimen of Quelch's Moseleya latistellata, the bottom consists of soft 

 mud the coral is flattened. The question whether M. has any genetic relation- 

 ship to the Cyathophyllida? is reserved for future consideration. 



