REPORT ON CORALS—HELIOPORIDA. 119 
The muscles in the autozooids are arranged with regard to the septa as in Heliopora, 
Pennatula, and Unibellula, showing a dorsal and ventral intermesenterial space. The 
protractor muscles are placed on the opposite sides of the mesenterial plates to those 
occupied by the retractors. Two mesenterial filaments are longer than the rest ; probably 
they are those of the “Dorsalfach,” since the only two retained by the siphonozooids are 
the dorsal ones. The ova are developed deep down in the autozooid cavities ; they have 
the usual form of the ova of Aleyonarians, and measure, when mature, about 7 mm. in 
diameter. They are placed in Plate I. fig. 2 at a greater height in the cavity of the 
autozooid than that at which they usually occur. Ova are to be found in the tubular 
prolongations of the autozooid cavities very deep in the colonies, whilst the tubular cavities 
of the siphonozooids have a diameter of about °35 mm. The autozooid cavities widen out 
beneath the surface to contain the autozooids and gradually contract again below ; they 
have an extreme diameter of 2 mm. 
Siphonozooids.—The siphonozooid cavities are only about one-fifth the length of 
the autozooid cavities. The siphonozooid cavities contract below and their tubes 
eradually narrowing join the canal-system, as is described by Kolliker to be the case in 
Sarcophyllum.. The siphonozoids (PI. II. fig. 3) consist of a simple globular stomach 
lined within by a thick epithelium, a prolongation of the ectoderm, and communicating 
with the exterior by a narrow tubular mouth; they have no trace of tentacles. The 
inner surface of the stomach is covered with long cilia directed downwards and 
inwards. Near the surface of the body, just beneath the ectoderm, eight mesenteries 
are present in all the siphonozooids ; but four of these extend to a much less depth 
than the others, and hence in a horizontal section at a very slight depth from the 
surface all the siphonozooids in section are seen with only four mesenteries, The 
four deeper mesenteries are those attached to the ends of the long axes of the 
stomach, 7.e., the dorsal and ventral. Only two mesenterial filaments, those of the 
dorsal mesenteries, are developed in the siphonozooids. The filaments are attached 
throughout their length to the margins of the septa. The siphonozooids are without 
sexual organs. 
Sarcosome.—The external surface of Sarcophyton is covered with an ectoderm 
resembling in structure that of Heliopora; it was not sufficiently well preserved in 
the available specimen to show its exact structure. No nematocysts were found in 
Sarcophyton. The mesoderm forms a general supporting mass consisting of tough, gela- 
tinous, transparent connective tissue, in which are distributed, somewhat sparsely, very 
small finely ramified nucleate corpuscles. In the walls of the siphonozooid and autozooid 
cavities, when viewed from their surfaces, there is to be seen a transverse fibrillation of a 
part of the mesodermic layer composing them; and these walls, when seen in section on 
1 Kolliker, l. c., 1 Abth. Taf. viii. fig. 68. 
