190 J. E. Duerden — Jamaican Actiniaria : 



A peculiarity connected with the Zoanthean filament is that the Flimmers- 

 treifen extend for some distance up each face of the perfect mesenteries, just 

 before the latter cease their connexion with the stomodeeum ; the middle portion 

 is folded and in actual contact with the mesentery, while the two ends, or at any 

 rate the centrifugal end, may hang freely in transverse sections. The whole 

 structure has been denominated by Haddon and Shackleton (1891, p. 619), the 

 " reflected ectoderm," these authors regarding it as representing a portion of the 

 stomodseal ectoderm which has become transferred to the face of the mesenteries. 

 In the adult the reflected ectoderm and mesenterial filaments are always found in 

 absolute continuity with the ectoderm of the stomodseum. And it has also been 

 demonstrated by M c Murrich (1891) and others, that even at an early stage in the 

 development of the embryo such a relationship can be recognized. 



While not inclined to accept the ectodermal origin of the " reflected ecto- 

 derm," or of any portion of the mesenterial filaments, the former term may be 

 employed for the present as referring to parts now well known in Zoanthean 

 morphology. The Hertwigs (1879) first emphasized the fact that trifoliate 

 mesenterial filaments may appear on mesenteries of the lower orders which never 

 reach the stomodeeum, and in all their structural details are indistinguishable 

 from those occurring on the first order ; and this appears to me to militate most 

 strongly against an ectodermal origin to any part of the Actinian filament. I 

 regard the continuity of the strongly ciliated stomodseal ectoderm, reflected 

 ectoderm, and the Fliminerstreifen and Driisenstreif of the mesenterial filaments 

 as having a physiological rather than a morphological significance, as being 

 necessaiy, in fact, for the proper maintenance and regulation of the internal 

 circulation of the respiratory and digestive fluids in the mesenterial chambers of 

 and around the stomodaeal region. 



The histological characters of the tissues point to this, while the similarity of 

 structure is not so great as is sometimes assumed. The uniform nature of the 

 cells composing the Flimmerstreifen certainly contrasts strongly with the variety 

 met with in the stomodseal ectoderm, with the exception of those lining the 

 gonidial grooves. The grooves are usually more strongly ciliated, and but few 

 glandular or stinging cells occur amongst the supporting cells. 



Less differences exist between the Driisenstreif and stomodseal ectoderm, 

 while the Entodermwucherung shows no histological relationship with the latter. 



The ciliation of the gonidial grooves, reflected ectoderm, and the Flimmers- 

 treifen is more pronounced than that of any other region of the Actinian polyp, 

 and usually persists in preserved specimens even when not observable elsewhere. 

 The histological elements are also more specialized, pointing to a specialized 

 function. The cells are almost entirely of the extremely narrow ciliated type, 

 each with an oval-shaped nucleus, often larger in diameter than the cell itself, 



