REPORT ON THE ACTINIARIA. 75 



which is thiu as paper, and through which the insertions of more than one hundred 

 and fifty septa are \dsible. The cinclides form a single circle at a little distance from the 

 pedal disk ; they are placed irregularly, sometimes higher, sometimes lower and closer to the 

 disk. Their walls rise above the surface in places like an hour-glass ; where this is not the 

 case they cannot be seen from the surface, and only become visible after the superficial 

 layer of the wall has been removed by a section parallel to the surface in the manner 

 already specified. Their number seemed to amount invariably to twenty-four ; they open 

 into the intraseptal spaces of the first three orders of septa. 



The circular muscle at the upper end traverses the entire mass of the wall, which is 

 trebly thickened at this point, but is separated from the endoderm by a narrow layer of 

 connective substance, from the ectoderm by a rather broader layer of connective 

 substance ; it is most powerful in the middle, and becomes weaker above and below ; 

 above, it reaches as far as the origin of the oral disk, where at the same time it most 

 closely approaches the two layers of epithelium. 



The bundles of muscular fibrillse show a tendency to arrangement in parallel layers, 

 placed one above the other as in Phellia pectinata (PL VI. fig. 5) and Cereus spinosus 

 (PL VI. fig. 1), though not so distinctly as in the latter species. Each layer again 

 consists of a number of smaller and larger groups of bundles of fibriUge, placed in a line 

 one behind the other, and each bundle, in transverse section, is divided by constrictions 

 of its surface iato lobes which are sometimes more, sometimes less distinctly separated 

 from one another. The muscular fibres which occupy the periphery and enclose the pro- 

 toplasmic axis in an undulating layer, are of medium strength. 



The arrangement of the bundles of fibriUse in layers becomes less distinct above and 

 below ; above, because the bundles are so pressed together that only a scanty framework 

 of the separating connective tissue trabeculse remains ; and below, because, on the other 

 hand, the bundles become very small and are isolated from one another. Finally, the 

 bundles of fibrillse become flatter from the outside towards the inside, but this is merely 

 in consequence of the contraction of the animal. 



The circular muscle of Calliactis polypus described above, is chiefly distinguished 

 from the circular muscle of Calliactis parasitica, which we have already investigated 

 (Actinien, p. 180), by not being divided into two distinct parts. There are also difiierences 

 in the muscular system, which enable us to distinguish the two species in a preserved 

 condition. I refer to the radial muscles of the oral disk, and to the similarly constructed 

 longitudinal muscles of the tentacles. 



The radial muscular fibres in Calliactis polypus form a thick layer which is always 

 thinned away above the insertions of the larger septa, and so divided into broader and 

 narrower radial bands. Their figure in transverse section is difiBcult to make out ; 

 at first sight it gives the impression that masses of compacted muscular fibres, 

 placed in repeated layers the one above the other, have been deposited between the 



