REPORT ON THE ACTINIA RI A. 55 



The oral disk is five-lobed, its periphery being delicately sinuated ; its upper third is 

 so thickly strewn with small tentacles that it is impossible to determine their number, 

 though we may estimate them at from two to three thousand; they are all very slender, 

 thin-walled, and caeca! ; they are largest towards the centre of the disk, and become 

 smaller towards the periphery. Twelve tentacles, which are particularly conspicuous 

 from their size, lie somewhat apart from the rest, nearer the centre of the oral disk, so 

 that they are isolated from the others. They are distributed at ecpaal distances round 

 the oral fissure in such a way that two of them correspond to the corners of the mouth ; 

 this mode of distribution leads us to conclude that they belong to the intraseptal spaces 

 of the six pairs of principal septa and the first six pairs of accessory septa. Outside these 

 come thirty-six other tentacles, which make up a circle ; twelve of these alternate 

 with the first twelve, the other twenty-four falling between the latter and the former. 

 The thirty-six tentacles can hardly be defined from the peripheral principal mass, because, 

 in the first place, there is hardly any interspace between them, and, in the second place, 

 because they are but slightly superior in size. They belong to the tertiary and quaternary 

 intraseptal spaces. By dissecting the septa, the peripheral mass of small tentacles may 

 also undergo examination, the result of which is to show that they all lie in different 

 radii of the body. We never find more than one tentacle in communication with the 

 same intraseptal space, though such a result seems highly probable on mere superficial 

 examination. All the tentacles belong primarily to a single circle, and have only been 

 forced into different circles by want of space. 



The radial muscular system, which in this case also lies in the mesoderm, shows the 

 same characters as those which we have already observed in the circular muscle. The 

 mesoderm is pleated in transverse section, and, in well preserved animals at least, is 

 covered with a layer of radial fibres ; the mesodermal bundles of fibrillse are flattened 

 and placed in rows which begin in the pleating on the surface of the mesoderm and run 

 straight towards the inside. We may say that we have before us deep laterally com- 

 pressed folds, which fall asunder into numerous bundles of fibrillse placed one below the 

 other (PL X. fig. 12). 



The layer of muscle is strongest between two septal insertions, and the mesoderm 

 consequently slightly thickened. In this way radial swellings are formed on the oral 

 disk, which, however, become more perceptible in transverse section than when looked at 

 from the surface of the oral disk, and more perceptible near the tentacles than in the 

 periphery of the mouth. 



The oral opening rises slightly like a proboscis above the surface of the oral disk, and 

 forms an oval fissure, one end of which is directed towards one of the points where the 

 margin of the oral disk arches inwards, and the other end to a point where it arches 

 outwards. The two oesophageal grooves are remarkably distinct on the oesophagus, as 

 they are enclosed by high lips, which project like combs, corresponding to which the 



