REPORT ON CORALS—HELIOPORID®. 1122 
There is no surface network of canals present in the superficial layer of mesoderm 
directly beneath the ectoderm, such as exists in Heliopora. 
The large canals in the stem of Sarcophyton, which are in reality long drawn out 
prolongations of the body cavities of the autozooids, may be considered as corresponding 
to Kolliker’s “sinus ;” the vertical and transverse canal systems to the “ canales nutrici 
majores ;” the network in connection more directly with the vertical systems to the 
“vasa nutrica minora.” Apparently there are no vessels corresponding to the “vasa 
capillaria,” their place being occupied by the network formed by the small ramified 
corpuscles in the sarcosome. 
The transverse and vertical canal systems anastomose with one another frequently, 
but only here and there. Occasionally, but rarely, the canals from the bottoms of 
the siphonozooid cavities join directly the transverse canals, The canals have a 
wall of fibrous tissue directly continuous with the fibrous layers of the siphonozooid 
and autozooid cavities, and are lined internally by endodermal cells (PI. IL. fig. 3, C). 
Sac-like enlargements or swellings are constantly to be seen on the canals of Sarco- 
phyton, -both near the surface and in the deep tissue. In one such swelling was 
found a parasitical cyst of oval form and with greenish contents; its nature could not 
be determined. 
Disposition of the Dorsal and Ventral Aspects of the Zooids——The autozooids 
in Sarcophyton are so disposed that they have the dorsal imtermesenterial spaces 
directed towards the centre of the pileus, and at the verge of the pileus these spaces 
uppermost. At least this disposition was observed to hold good in three opposed 
radial directions from the centre of the pileus. A whole specimen was not available for 
examination. 
As in Heliopora the autozooids are not disposed with perfect regularity in this 
manner, so that radial lines from the centre of the pileus would pass directly through 
their longer diameters. Many of them are rotated more or less on their axes, so as to be 
inclined to the radial lines. They are most regular in disposition at the margin of the 
pileus. The siphonozooids, though preserving a general uniformity of arrangement, 
which proves their single pair of mesenterial filaments to be the dorsal ones, are still 
more irregular in disposition. 
GENERAL REMARKS. 
Affinities of Heliopora.—Heliopora is most undoubtedly an Aleyonarian. The 
number of its mesenteries, and the distribution with regard to them of the retractor 
muscles, the form and number of its tentacles, are decisive evidence in the matter; and 
this evidence is borne out by almost every item of histological structure. In the peculiar 
manner in which the retraction of the tentacles takes place, viz., by introversion, Heliopora 
(ZOOL. CHALL., EXP.—PART VIL—1880.) G 16 
