190 J. H. ASHWORTH. 



forming one stem of the colony. The external characters of the free 

 portion of the polyp have been described above. The eight mesenteries 

 of the polyp are arranged as in typical Alcyonaria. On their ventral 

 faces they bear the retractor muscles, and on the opposite faces the 

 protractor muscles, neither of which are well developed. This some- 

 what feeble development of retractor and protractor muscles accounts 

 for the non-retractile nature of the polyps. The iutermesenterial 

 spaces are continued upwards into each tentacle and into each pinnule. 

 In the free portion of the polyp, and particularly in the tentacles and 

 pinnules, these spaces are to a large extent filled up by zooxanthellse. 

 The specimen is a male, and in the lower part of the free portion of 

 the polyp, and in the upper part of the stem, the coelentera are crowded 

 with sperm-sacs containing spermatozoa in all stages of development, 

 from the small masses containing only two or four primitive sperm- 

 cells to the large mature sperm-sacs containing mauy hundreds of ripe 

 spermatozoa. 



Mesogloea, its Canals and Cells. — In the stems the coelentera of the 

 polyps are bound together by a moderately large quantity of mesogloea. 

 The mesogloea immediately round each polyp is slightly denser than 

 that further away, so that in transverse sections of the stem, especially 

 if the sections be taken through the upper part, one can distinguish 

 the more deeply staining ring of slightly denser mosogloea, which defi- 

 nitely belongs to the ccelenteron within it, from the less dense mass of 

 mesogloea between these rings, which cannot be assigned to any polyp 

 or polyps (Plate XX., Fig. 9). Traversing the mesogloea of the stem are 

 numerous canals, cords and strands of cells, which place all the parts 

 in intimate communication with each other. The canals may be 

 divided into tw r o systems— a superficial system and an internal system. 



The superficial canal system (Figs. 8, 9, Sup. Can.) is formed by a 

 plexus of numerous endodermic canals, which are situated in the outer 

 portion of the mesogloea, just beneath the ectoderm of the stem. This 

 system of canals extends all round the cylindrical stems, and also runs 

 on the umbrella-shaped areas from which the free portions of the polyps 

 arise (Fig. 8). The cavity of this system of canals is invaded through- 

 out by zooxanthellse, which are especially numerous in the canals in 

 the upper part of the stem. 



