ACTIMAN BUXODEOPSIS GLOBULIFEEA. 301 



the cell- contents stain deeply, being highly protoplasmic, and Zooxanthellae are absent 

 or nearly so ; where the layer is broader the cells are more vacuolated, the free surface 

 is somewhat irregular, and the symbiotic alg;3e are found in large numl)ers. Throughout 

 the endoderm of the polyp similar broad and narroAV areas are represented, according as 

 Zooxanthella? occur inal)undance or ai*e practically absent. A weak circular endodermal 

 musculature can be detected on the base, and in some specimens a nerve-layer separated 

 from the muscle-band by a fibrillar layer. Tiie latter, however, was not recognizable 

 in the section from which fig. 2 was taken. 



Column-wall. 



The proximal and distal regions of the column-wall vary somewhat in structure. The 

 former is broad and irregular in outline, owing to the occurrence of the evaginatious. 

 while the naked area is verv thin and delicate, measurini? in sections onlv '03 mm. 



ft ' o » 



across (fig. 4). 



The ectoderm of the column-wall is weakly ciliated throughout, and both transverse 

 and vertical sections of the upper part otten exhibit fine ridges and grooves as a result 

 of uneqvial shrinkage (fig. 3). These appearances, however, are more characteristic of 

 the tentaciilar ectoderm, as shown in the same figure. The constituents are mainly 

 supporting cells and clear gland-cells ; nematocysts occur very sparingly, except in the 

 evaginatious of which they are very essential elements. A layer of delicate ectodermal 

 muscle-fibres occurs throughout the extent of the column, and in some places the meso- 

 gloea IS very slightly plaited for its support. The muscle-fibres are arranged with the 

 long axis vertically, so that they are cut cross-ways in transverse sections of the polyp, 

 and constitute a delicate but clearly-marked layer, the fibrils being highly refractive. 

 Outside the band of muscle-fibres occurs a weak nerve-layer {iir.l), the two distinctly 

 separated by a narrow interval crossed by fine fibrillar strands (figs, 3. 5, 16). 



The natu.re of the fine strands occurring between the band of muscle-fibres and the 

 nerve-layer, and continued in some cases beyond the latter, is not readily determined. 

 They occur practically throughout the polyp, on both the ectodermal and endodermal 

 surfaces, but are much more definite in some individvials than in others. McMurrich 

 (1890. p. 113) refers to a somewhat similar appearance in various parts of the body- wall 

 of Cerianthus americanus, and regards the processes as mesogloeal prolongations. 

 Carlgren (1803, p. 26) describes a nearly similar structure in ProtanUtea simplex, and 

 also considers it to be due to very fine continuations of the mesogloea, which here and 

 there bear strongly refractive bodies, resembling sections of muscle-fibrils. In Carlgren's 

 preparations the details A-ary greatly according to the manner of preservation of the 

 specimens, and McMurrich' s two specimens of Cerianthus likewise diflfered. 



The specimens now under consideration were preserved in formol and then transferred 

 to alcohol, and the interval between the mesogloea and the ganglion laj'er varies greatly 

 in width in different polyps, and even in different regions of the same individual. 

 Usually it is more pronounced on the endodermal side than on the ectodermal, and on 



