REPORT ON THE ACTINIARIA. 59 



The surface of the oral disk is smooth, or only indistinctly furrowed radially ; if ex- 

 amined in transverse section (fig. 5) it shows a set of strong mesodermal muscles, a broad 

 baud, separated both from the endoderm and the ectoderm by a layer of supporting 

 substance. This band is broken by a separating bar of connecting substance, correspond- 

 ing to the insertion of every septum. It is further a law of its development that the 

 sup]3orting substance grows out strongly into the muscular band from the endodermal and 

 ectodermal sides alternately, and forms ridges from which ramified supporting layers 

 stretch towards the opposite side. In this way smaller and larger elongated compartments 

 are formed, which are filled with muscular fibres. These muscular fibres, like those of the 

 wall, are extremely thick, and the manner in which they pass on to the tentacles dis- 

 tinguishes the Ophiodisci sharply from other Actiniae. 



Although the tentacles were badly preserved, it was perfectly clear that they are thin- 

 membraned on one side but thickened on the other (fig. 2). This thickening is caused 

 by a muscular cord which can be followed even with the naked eye as a broad fibrous 

 streak running from the oral disk to the tentacle. It occupies that side of the tentacle 

 which is turned upwards in a state of rest, and projects at its base right and left a little 

 above the surface. It thus forms two wing-like expansions which pass a little way on to 

 the oral disk. The structure of this cord is the same as that of the muscular band of 

 the oral disk ; it is composed of strong, thickly compacted muscular fibres, divided by thin 

 layers of connective substance into compartments of muscular fibres. 



Muscular fibres are wanting in the thin membraned parts of the tentacles, unless 

 they be present in the ectoderm, which could not be determined, as the ectoderm was 

 completely macerated away. Whilst the muscular cord passes into the oral disk, the thin 

 membraned parts of the tentacles, on the other hand, are prolongations of the wall. This 

 is brought about by the fact that the tentacles lie exactly on the border line at which 

 wall and oral disk are united. 



Before passing into the oesophagus, the oral disk is raised in the periphery of the 

 mouth into a proboscis-like projecting lip. The proboscis is marked on either side with 

 about ten longitudinal furrows, and is likewise furnished with two oesophageal grooves, 

 which are enclosed by two strong longitudinal folds, hard as cartilage, and pass downwards 

 on to the long oesophageal lappets. In one specimen the lower part of the oesophageal 

 grooves appeared closed into a tube by fusion of the margins of the folds. 



The number of the septa amounted in all to forty-eight pairs, which are distributed in 

 four cycles. The first three cycles, that is, the fixst twenty-four pau's, are formed exclu- 

 sively of muscular septa which do not bear reproductive organs ; of these the septa of 

 the first two cycles only reach the oesophagus, the remaining twelve pairs are imperfect. 

 Septal stomata are wanting. The muscles are slightly developed, for I could not even find a 

 parietobasilar muscle. In consequence of insufiicient preservation, the free margins of the 

 septa had become frayed out, and only part of the mesenteric filaments remained (fig. 4). 



