172 J- E. DuERDEN — Jamaican Actiniaria : 



while some of the free pairs were attached liigher up. The members of the fourth 

 cycle extended only a short distance from tlie column-wall. It would thus appear 

 that the normal arrangement of the mesenteries in the stomodseal region of young 

 polyps is as follows : — the first cycle of twelve pairs of perfect mesenteries consti- 

 tutes the first and second orders ; a second cycle is formed of twelve alternating 

 pairs; and a thii'd cycle of twenty -four pairs. Beyond this irregularities begin to 

 step in. In older specimens many more than twelve pairs become united with the 

 stomodaeum. The region of the directives is always that of most forward growth. 

 The mesenteries present a concave outline as they cease their connexion with 

 the stomodseum, so that in sections through the lower region of the latter the free 

 edge of the mesenteries, bounded by a mesenterial filament, appears twice, one 

 part being in connexion with the column-wall, and the other, shorter part with the 

 stomodseum. The six mesenteries of the second series become free in advance of 

 those of the first. 



The retractor muscles extend across nearly the whole face of the mesentery, 

 but are nowhere much thickened, resembling somewhat those of aS*. hcliantlms. 

 They differ in this respect from those of A. elegans, wliich are circumscribed and 

 project considerably. 



The parieto-basilar muscle is strongly developed on both faces, and supported on 

 numerous fine mesogloeal plaitings, but a separate pennon is not present, at any rate 

 in the upper region. The nervous layer and fibrilloe are very distinct in this region. 

 The retractor muscle commences abruptly and extends along the greater part 

 of the face of the mesentery, terminating more gradually centripetally. The 

 mesogloeal processes are long, narrow, and branching, and constitute neai'ly the 

 whole of the thickness of the mesentery. The endodermal epithelium is very 

 narrow comparatively, and contains numerous granular gland cells. There is little 

 trace of any oblique musculature. The mesenteries are very narrow beyond the 

 retractor region. 



The mesenterial filaments are typical in character, closely resembling those of 

 Phymanthus crucifer, already described. The trilobed condition occurs on the first 

 two or three cycles, and is continued for but a short distance below the aboral 

 termination of the stomodseum. The Nesseldriisenstreif or glandular streak at the 

 apex of the middle lobe, is very limited in its extent, and the first portion of the 

 intermediate streak is characterized by an abundance of small zooxanthellse. The 

 Flimmerstreifen or ciliated streaks also occupy but a small region of the lateral 

 lobes. The cells of the reticular streak contain but little pi'otoplasm, while the 

 mesogloeal axis in all three lobes is crowded with small, deeply-staining cells. 



Below the stomodseum the mesenteries branch considerably at their free 

 extremity, each division being terminated by a simple, more or less rounded 

 filament. As each side of the filament approaches the mesenterial epithelium, its 



