REPORT ON CORALS — HELIOPORID^. 119 



The muscles in the autozooids are arranged with regard to the septa as in Heliopora, 

 Pennatula, and Umbellula, 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 Alcyonarians, 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 

 gradually narrowing join the canal-system, as is described by Kolliker to be the case in 

 SctrcophyUiim. 1 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, i.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, J. c, l te Abth. Taf. viii. fig. 68. 



