REPORT ON THE ACTINIARIA. 99 



The wall is small in height, and divided by a deep circular constriction into 

 an upper and a lower half (fig. 9) ; it appears, on the whole, smooth and only- 

 furrowed irregularly on the surface in consequence of the contraction of the 

 animal. The cii'cular layer of fibres on the inside is very M^eak, both because the 

 separate fibrillse are very fine, and because the layer, formed by them, is only slightly 

 pleated. The circular muscle at the margin of the peristome is also insignificant ; 

 it lies immediately outside the tentacles, and produces about four or five narrow 

 circular swellings on the inside of the wall (fig. 1). It belongs completely to the 

 mesoderm, in which it is embedded as a very narrow streak, close under the endoderm. 

 The fibrillse, like those of the wall, are very fine, and united in small bundles which lie 

 close to one another, and are only separated by a small amount of intervening substance. 

 In transverse section, and under weak magnifying powder, the muscular layer therefore 

 presents the appearance of a finely granulated mass. 



The most important parts for the definition of the species are the oral disk and its 

 tentacles. The surface of the oral disk is marked by sixty- four radial furrows, which run 

 from the swoUen margin of the mouth towards the bases of the tentacles, and are caused 

 by the attachments of the septa. They are, moreover, correlated with the arrangement 

 of the radial muscles, the layer of which always either becomes thinner or is completely 

 interrupted along a line below every furrow. The muscles are further mesodermal, 

 and so deeply embedded in the supporting lamella that they lie at equal distances from 

 the endodermal and the ectodermal surfaces. The separate fibrillge (fig. 6) are very 

 powerful, and the way in which they are grouped gives rise in transverse section to a 

 figure recalling the conditions known in the vertebrata. A few fibrillae are closely com- 

 pacted into a primitive bundle, several such bundles unite to form a secondary bundle 

 (fig. 8), and these again are united into larger groups. Each portion of the muscular 

 layer lying between two radial furrows contains several groups of such bundles. 



There are sixty-four tentacles in all, distributed in two alternating circles. They 

 present a very unusual appearance, and are short knob-like elevations with a broad oval 

 base, and are pierced by a wide opening at the point. This gives them the appearance 

 of sucking cups, and on this account I have named the animal Sicyonis. The surface is 

 repeatedly pleated, and the interior also shows distinct circular folds (fig. 9). The walls 

 are very thick as far as a thin margin surrounding the terminal opening (fig. 3). 

 The radial muscular fibres of the oral disk make their way as longitudinal cords into the 

 tentacles, and have the same arrangement in the middle of the broad layer of connective 

 tissue as we have already discussed in the description of the oral disk. Examined in 

 transverse section (fig. 5), they are deposited in a ring, which, however, is interrupted on 

 the side turned towards the margin of the peristome. There the layer of connective tissue 

 is very thick, but only contains a few isolated bundles of muscular fibriUse. We see, 

 moreover, in longitudinal section (fig. 3), that the cords of muscular fibres do not make 



