268 J. H. ASnWORTH. 



lie close to the ectoderm, while others are near the endoderm. 

 They are connected together by their exceedingly slender pro- 

 cesses, which traverse the mesogloea and unite with each other. 

 These cells resemble, and are probably homologous with, the 

 nerve-cells and nerve-fibres of Alcyonium and the Actinise. 

 They will be further described below (see p. 277). The 

 mesogloea of the mesenteries and its included cells have already 

 been described (see p. 263). 



2. Of the Stem (see PL 25, figs. 8 and 9). — On examining 

 transverse sections of the upper portion of the stem there is 

 seen a slightly denser ring of mesogloea {Mg. D.) around each 

 of the coelentera. This ring of denser mesogloea is itself 

 moderately free from cells, being crossed only at intervals by a 

 cell or thin cord of cells, but it is bordered by an almost com- 

 plete cordon of cells, interrupted only for the passage of 

 endodermic canals. The canals of the stem are moderately 

 .arge and very numerous, being much more highly developed 

 than those of Alcyonium. The canals may be divided into 

 the two systems described below. 



The Superficial Canal System. — This system of canals 

 is formed by numerous endodermic canals (Sup. Can., figs. 8 

 and 9) which are situated in the stem about "1 mm. beneath 

 the ectoderm. This system is really a fine network of 

 numerous canals, which have a similar structure and appear- 

 ance in all parts of the colony. The canals are about '08 mm. 

 in diameter. In the intervals between these canals there are 

 usually cords of ectoderm cells {Ed. Str.) which pass from 

 the ectoderm to cells in the deeper parts of the mesogloea. In 

 many cases the superficial endodermic canals are themselves 

 closely connected with the ectoderm by strands of cells passing 

 across the mesogloea from the ectoderm to the outer walls of 

 the canal lying beneath. From the inner wall of these canals 

 cords of cells frequently pass inward into the mesogloea, and 

 are connected with other cells, with the coelentera, or with 

 longitudinal canals. 



The superficial canals are also present on the convex summit 

 of the stem (sec fig. 8), and form there a plexus of canals, 



