REPORT ON THE HEXACTINL^ 25 



Internal Strtictiwe. — The mesogloea of the column wall is, 

 relatively to the size of the individuals, rather thin and is pro- 

 vided with a well-developed circular musculature, whose general 

 appearance resembles that of C. clegantisshua. In the upper part 

 of the column, however, it is comparatively poorly developed, 

 and also on the inner walls of the evaginations which produce 

 the verrucse, being entirely wanting at the apex of these. 



The sphincter (Fig. 18) is large and is of the pedunculate bi- 

 pinnate type, the lateral lamellae of one side being, however, 

 stronger than those of the other so that it is properly described 

 as unequally bipinnate. In one of the three specimens a deep 

 incisure occurred on one side of the sphincter, reaching almost 

 to the median axis and giving the section of the sphincter a 

 reniform outline. This was wanting, however, in the other two 

 in which the sphincters were oval in section. 



The tentacles are not ridged and have a well-developed, though 

 simple, ectodermal musculature. Their endoderm, as well as 

 that of the disk and of the upper part of the column wall, is 

 richly laden with granules of black pigment, insoluble in the 

 reagents employed in hardening and sectioning. The ectoder- 

 mal musculature of the disk (Fig. 18) resembles that of the ten- 

 tacles, being supported on well-developed simple or but slightly 

 branched processes of mesogloea. 



Two siphonoglyphes are present and the walls of the stoma- 

 todaeum are longitudinally ridged and in addition considerably 

 folded. 



The mesenteries are arranged in four cycles and there are in 

 all forty-eight pairs (6, 6, I2, 24). In sections through the 

 upper part of the column all but those of the fourth cycle are 

 seen to be perfect, but below the level of the stomatodaeum the 

 various cycles can be distinguished by the relative breadths of 

 the various pairs, those of the first and second cycles being how- 

 ever nearly similar in this respect. The mesenteries of' the 

 fourth cycle do not bear mesenterial filaments and there are two 

 pairs of directives, placed symmetrically. 



The longitudinal musculature is well developed (Fig. 19), 

 covering almost half of the non-gonophoric portion of the 



