218 CTENOPIIOR^E. Part II. 



liarallelly in the flapper, and that their outer free ends constitute the marginal 

 fringe of this organ, and furthermore that each cell is as it were a single tooth 

 in the comb-like flapper, reaching in one stretch from the base to the margin. 

 Thus the locomotive flappers -would Ije formed by the simple projection of these 

 cellnlo-motory vesicles beyond the surface of the body,^ and by their arrangement 

 in a single row, combined with lateral coalescence. As these cells are simple pro- 

 longations from the midst of other similar cells, we should take it for granted that 

 they have similar motive powders ; for no action of special muscles — supposing that 

 they were present, which is not true — could be so transmitted from the base 

 along the flapper as to give it that peculiar curve which it frequently assumes 

 when in a stationary condition : but any one may understand how the cells them- 

 selves can assume such a curve, and that each combined row of cells moves by 

 the inherent power of its components, for, as we have frequently oliserved, when 

 the flap])ers are minutely split up from edge to base, each cell viljrates isolatedh', 

 and either in consonance with the others or at random. 



It has oftentimes been noticed by observers, that whilst Pleurobrachia is in a 

 dying state and even tailing to pieces, and the epithelial cells peel off from the 

 body, and, as we have observed, from the flappers too, in the form of a filmy 

 mucus, the flappers themselves remain to the last moment flajiping convulsively, 

 wdierever there is a bit of the body to which they may adhere, thus showing their 

 intimate connection with the deeper seated cells. The ganglion-like Ijodies described 

 in my former paper on Boroid Medusce are nothing but the points of convergence 

 of several such cells : they are very irregular in shape, and not always to be seen. 



The remarkable iridescence of the flappers, we tliink, can Ije easily explained )jy 

 reference to Avhat we now know of their intricate structure. Each cell being 

 excessively flattened, the walls are approximated like superposed laminae, and these, 

 with the surfaces of the epithelial cells, form all that is required to produce the 

 same kind of action upon light as a pile of thin plates of mica or glass. 



The tentacular sockets {F/;/- 15 / j^) are embraced by a wall whose cellular 

 constituents closely resemble those of the interambulacral system ; and, in fact, as 

 will he shown hereafter in detail, these sockets are nothing more nor less than 

 deep depressions in the latter system : the cells trend in the same general direction, 

 that is, their longer axes trend transversely to the length of the sockets, and, for 

 nearly one half of their distal extent, from the base of the tentacles [//) to the 

 aperture (y^), completely encircle them, like a constrictor muscle. At the basal 

 half of the .sockets, these cells form only a semicircle {F/ff. 15 / J", Fiij. 21 if') on 



' Tlii.s lieing true, the locomolive fVingos are in posed before I knew fully tlicir structure, and as 

 no way ooiniiarable to vibratile cilia, as I bad sup- Will also admitted. 



