558 



find a gradual transition from the linear budding of Zoanthus proper 

 to the aggregation of the polypes in some species of Palythoa, but 

 in the typical members of the latter genus, the Polypes are not only 

 connected at the base, but have their bodies also severally united so 

 as to form a solid mass ; and a more decidedly compound nature exists 

 in them than we find in any of the varieties of the present species ; 

 so that, although partaking of the characters of both genera, Zoanthus 

 appears to be the one to which this is most nearly allied. An evident 

 approach to the same intermediate form may be observed in the 

 reticulate arrangement of the connecting bands of Z. bertholetii from 

 the Red Sea. 



In our British species, the body forms a cylinder from 2 to 4 lines 

 high, by about half that in breadth, and is clothed with a dense 

 coating of fine sand, which at the upper extremity is divided into 

 14 deeply-cut marginal teeth; these cover the top of the column 

 when the animal is closed, but are turned a little outwards during 

 expansion. The tentacula are moderate in length, slightly tapering, 

 smooth, and not capitate ; they are arranged in two rows containing 

 14 each, of which the inner series are rather the longer, and are 

 placed opposite the angular prolongations of the column, those of the 

 outer row alternating with them. Fourteen tentacles in each row 

 appear to be a character of specific value, as I find that number con- 

 stant in specimens of various sizes, and they correspond with the 

 marginal divisions. The disk (fig. 7), which is generally concave, some- 

 what exceeds the diameter of the body ; and the prominent mouth 

 opens with a simple linear orifice. The general colour of the disk and 

 tentacula is a pale transparent brown, becoming opake white around 

 the mouth and at the tips of the arms ; and all the intermediate 

 parts are finely speckled with the same tint. At first sight, the ten- 

 tacles appear to be knobbed as in Corynactis and some of the Coral- 

 ligenous Polypes ; but their form is really quite simple, and the 

 capitate appearance of these organs is due solely to the conspicuous 

 colour of their extremities. 



Among the external characters of this family, the serrated margin 

 of the column is remarkable, but an examination of the animal shows 

 that this structure is a simple provision for enabling a polype so 

 peculiarly coated to close its disk perfectly, and in the contracted 

 state to be completely protected by its sandy covering. Closure of 

 the disk in the soft-bodied Actiniae is effected by the action of the 

 muscles surrounding the upper extremity of the body ; and as the 

 skin is soft and yielding, contraction takes place equally on every 

 side, and is continued until the edges of the column meet in the 

 centre. In Zoanthus, the case is different ; fine sand being densely 

 impacted into the epidermis, little or no contraction can take place, 

 and the polype would be unable to close in the usual manner if this 

 hard covering were uniformly extended to the margin of the disk. 

 Under the microscope, the wall of the column is seen to terminate in 

 a number of triangular processes or teeth (fig. 6), united at the base, 

 and covered externally with sand like the rest of the body ; these pro- 

 longations are connected throughout their length by a thin membrane, 

 which is crossed by the ordinary transverse muscles, whose contraction 



