176 J. E. DuERDEN — Jamaican Actiniaria : 



though a sHglit disparity occurs in that forty-eight rows occur, while there are 

 twenty-five pairs of mesenteries, forming, of course, fifty mesenterial chambers. 

 The disc overhangs the cokimn a little, and can be almost completely retracted. 



The base presents a very delicate opaque whiteness, and nearly the whole 

 superficial area of the column shows a similar opacity, particularly evident in 

 the upper region ; clear and transparent areas may, however, remain in places, 

 as at the verrucse. In the more distal region some of the ridges may be a delicate 

 transparent brown. The colours of the knobs of the tentacles are variable, and 

 not arranged according to any definite pattern. They are mostly opaque white, 

 with various mottled colours on a clear transparent ground ; spots of yellow, brown, 

 pink, red, and white are irregularly mingled. The marginal tentacles are more 

 spotted with opaque white than are those more internal. Preserved in formol 

 the specimen changed its colour as a whole to a dark brown. 



The column may extend to as much as 15 cm. (6 inches) in height, and is 

 about 5 cm. in diameter. 



Anatomy and Histology. 



The ectoderm of the base is an exceptionally deep layer. Large numbers of 

 long, unicellular glands occur of about the same diameter throughout, and 

 contain finely granular matter. 



The mesogloea is narrower than the outer layer, and is slightly fibrous in 

 character ; numbers of small cells are included within it. Internally it is finely 

 plaited for the support of the endodermal muscle, which is here feebly developed. 

 The endoderm is the narrowest of the three layers, and presents irregular 

 internal limitations, and many granular gland cells. 



The column- wall is much and deeply folded, and of moderate thickness in 

 each of its three layers. Peripherally the ectoderm appears somewhat dense, 

 owing to the great abundance of unicellular glands with finely granular contents ; 

 the cells extend from the inner limits of the layer, but become more swollen 

 towards the outer surface. Though the polyp was nearly transparent when alive, 

 the column-wall changed to an opaque dark brown on preservation in formalin, 

 and the contents of the ectodermal cells apjjear yellowish brown on microscopic 

 examination. The nuclei of the ectodermal supporting cells are mostly 

 aggregated within a middle zone, and a slight ectodermal musculature is 

 developed. 



The fibrous nature of the mesogloea is more obvious in the column than at the 

 base, and the layer is very irregular in its outline, giving rise to numerous, deep 

 folds on both its outer and inner aspects. On its endodermal border it forms, in 

 addition, long, narrow, branching processes for the support of the strong, 



