REPORT ON CORALS—EXPLANATION OF PLATES. 235 
. 2, Transverse section through the uppermost part of a retracted polyp of Heliopora 
cerulea, as viewed from below, showing the under surface of the most super- 
ficial structures closing the mouth of the calicle, z.e., the immediate under 
surface of the polyp-lobes seen in Plate I. fig. 5, and Plate IL. fio. 1. The 
drawing is from a decalcified preparation. The soft parts lining the wall of 
the calcareous calicle are cut through; they retain the form of the calicle, 
to which they were closely applied. The wall presents a series of longi- 
tudinal folds so as on transverse section to show a sinuous outline with 
twelve indentations separated by twelve bulgings. The indentations occupied 
in the fresh condition of the animal by calcareous matter represent the 
twelve ridge-like calcareous septa present in the calicle. The indentations 
are neither in form nor arrangement symmetrical, nor are the eight mesen- 
teries (MM) arranged symmetrically with regard to them. 
Between the mesenteries the body-wall of the polyp does not reach out- 
wards everywhere the entire distance to the wall of the calicle, but is con- 
tinuous with this only in the region of its indentations. At each of the 
bulgings of the wall a wide aperture is left, by which the cavity of the polyp 
communicates with the canal systems around. 
MM. Mesenteries. 
OO. Openings by which the polyp cavity communicates with the canal- 
systems. The light oval spaces shown in the shaded areas of the 
openings are the sinus of the superficial canal-system. 
Fig. 3. Vertical section through one of the siphonozooids of Sarcophyton. On the left- 
hand side of the drawing the caleareous spicules are shown in situ. On the 
right the appearance presented after these have been removed by acid is shown. 
The points of the spicules accompanied by a layer of connective tissue 
project up far into the prominent layer and raise it up just as do the external 
ectodermal points of hard tissue in Heliopora. The connective tissue shows 
excessively small ramified nuclei scattered through its otherwise homogeneous 
tissue. Portions of adjacent siphonozooid cavities are shown on either side 
of the central one ; the transverse fibrillation of their wall is indicated. 
Sp. Spicules. 
S.C. Cavities from which spicules have been removed by acid. 
8. Stomach of the siphonozooid provided within with cilia directed inwards. 
ME. Its mesenteries.: 
MF. Mesenterial filaments. 
C. Canal of the transverse system, forming a communication between two 
adjacent siphonozooid cavities and lined by endodermal cells con- 
tinuous with the layers lining the siphonozooid cavities. 
