REPORT ON THE ACT1NIARIA. 31 



The radial muscles of the oral disc are ectodermal, and form a slightly pleated layer ; 

 a notable point is the presence of small bundles irregularly embedded in the mesoglcea. 



The number of mesenteries appears on macroscopic examination to be confined 

 to twelve, set a.t equal distances on the periphery of the stomatodaeum ; they are so 

 grouped in pairs according to the muscular distribution, that one can distinguish two 

 pairs of directive and four pairs of intermediate mesenteries. They resemble thin 

 veils stretching between body-wall, oral disc, and stomatodseuru, unusually delicate, and 

 tearing at the slightest strain ; below, they reach nearly to the posterior pole of the 

 body, but are here so weakly developed as to hardly project at all into the coelenteron. 



In these veil-like mesenteries are recognisable, as special thickenings, the following 

 organs: — 1, the muscle pennons or retractors; 2, the muscles of the edge; 3, the 

 generative organs ; 4, the digestive filaments. 



The retractors are powerful swellings about 1-2 mm. wide, which are tolerably 

 sharply bounded, and appear as if glued to one side of the mesentery ; they commence at 

 the angle where oral disc and stomatodasum are continuous, and run from this point in 

 a slight curve outwards and downwards to the boundary between the first and second 

 thirds of the body-wall, where they terminate, thus dying out disproportionately soon, 

 far sooner than even in Ilalcarrvpa claims. Transverse sections exhibit their structure 

 in greater detail ; in the region of the muscle the supporting lamina is strongly 

 thickened, and is elevated, together with the muscle-layer resting on it, into lamellae 

 which are long, thick, and parallel to one another, but which either do not branch at 

 all, or only slightly. An arborescent or bush)^ appearance is occasionally produced by 

 a ridge of the mesogloeal mesenterial lamina bearing on both sides a complete series 

 of muscular lamellae. The sharp boundary of the muscular masses is referable to the 

 circumstance that on both sides the pleating of the muscular layer ceases abruptly. 



The edge-muscles form a band of tendinous appearance running close along the 

 body-wall, and are most clearly expressed in the posterior parts of the body. Here 

 they constitute nearly the whole of the mesentery, and the mesenterial filament is 

 affixed almost directly to them. 



The mesenterial filament is fairly obvious for the first two centimetres below the 

 stomatodaeum, and is arranged in a few coils. Afterwards it becomes finer, but is 

 wound into a mass of twisted loops, continuing thus for about the next four centi- 

 metres. The contortions then become gradually less marked, till, sooner or later, the 

 whole filament dies out ; in one mesentery it could be followed to within two centimetres 

 of the posterior pole. The first section of the filament is trilobate, possessing one 

 glandular and two ciliated lobes ; lower down it undergoes, as in other cases, a simpli- 

 fication of structure by the dying out of the ciliated lobes. 



Both the glandular and the ciliated lobes are of exceptionally strong development ; 

 the continuations of the mesogloeal lamina entering them broaden out in the shape 



