52 MRS. LEONORA J. WILSMORE ON SOME 



Disc (PI. 6- fig. 19, (L). — The musculature o£ the disc and tentacles in the 

 former species alike, are in this species very different. The ectodermal 

 muscle of the disc is only slightly developed and strongly resembles that of 

 Phellia sollasi (20), another Australian species. A few mesogloeal processes 

 are present peripherally. More centrally these processes are absent and the 

 muscle very feebly developed. The endoderm is narrower than in the 

 tentacles and very few nematocysts are present in the ectoderms. 



Mesenteries and Acontia (PI. 6. fig. 17). — There are three cycles of 

 mesenteries, the formula for each sextant being the same as in the last 

 species, viz. PiilhiP. The perfect mesenteries are of the first cycle only, 

 number six pairs including the directives, and carry the gonads ; there are 

 also six pairs of imperfect mesenteries of the second and twelve pairs of 

 imperfect of the third cycle. 



Perfect mesenteries. A surface view of the distal part of a perfect mesentery, 

 as it appears on opening the anterior end of the polyp longitudinally, is shown 

 in PL 6. fig. IG. It will be seen that the longitudinal retractor muscle has a 

 most unusual form. Throughout the greater length of the mesentery it 

 consists of a muscle-pad of uniform and very narrow width (PI. 6. fig. 16, 

 m.p.), but at its distal extremity it increases suddenly in size and ends in a 

 large bulb or head (PL 6. fig. 16, m.b.). The oesophagus, which is attached 

 to the perfect mesenteries and does not extend below the level of the enlarged 

 heads, has, in eversion, drawn the mesenteries upwards and outwards. The 

 position of the heads of the muscle-pads in the lobes of the everted 

 oesophagus is due to this fact, and their curvature probably arises from the 

 same cause. 



The internal structure of the muscle-pad and its enlarged head are shown 

 and compared in PL 6. figs. 17, 18, & 19. In longitudinal and transverse 

 sections of the head (figs. 18, 19) it will be seen that the structure consists 

 entirely of very numerous delicate processes branching from a mesogloeal 

 core, the muscle-cells being situated on these processcn. The muscle-pad 

 shown in transverse section (fig. 17, m.p.) is drawn on the same scale as the 

 muscle-head in fig. 18. In structure the muscle-pad difters from the muscle- 

 head only in the fact that the mesogloeal core is much slighter in the pad 

 and does not penetrate so deeply. In shape also the transverse section of the 

 pad is more reniform than that of the head. 



The marked difference in the form of the retractor muscle in this species 

 and in Phellia broivni may be seen by comparing fig. 10 on Plate 5 with 

 hg. 16 on Plate 6. 



The mesenterial filament is very small ; immediately below the oesophagus 

 it is divided into three parts ; lower down it is single (PL 6. fig. 17, 

 me.^^. 



The parieto-basilar muscle, which is present in the perfect mesenteries 

 only, forms a well-developed brush-like tuft on that side of the mesentery 



