BEANCHIOCEEIANTHUS IMPERATOK (aLLMAn). 245 



series of sections (PI. XV Figs. 4-9) passing through the lines 1-1, 

 2-2, 3-3, 4-4, 5-5, 6-6 in Fig. 1, PL XV is introduced. The 

 first section (Fig. 4) through the outermost margin of the disc, 

 which corresponds to the line 1-1 in Fig. 1, shows that the bases 

 of the marginal tentacles (Lb.) and the blind ends of the radial 

 canals {r.c.) are arranged alternately, the former projecting out 

 above and below more than the latter. The upper projection 

 corresponds to the enlarged end of the solid cord. The cavity 

 of the tentacle is almost filled up by the spongy endoderm which 

 lines the whole cavity of the animal, so that it remains as a 

 narrow canal only in the upper and lower sw^oUen parts of the ten- 

 tacles. On the other hand the radial canals contain a wide cavity 

 which is clearly separated from that of the tentacle-base by the 

 well developed mesoderm. In the next section (Fig. 5, through 

 the line 2-2, Fig. 1) cut just inside the margin of the disc, the 

 radial canals already assume their characteristic shape in cross- 

 section, while the intercalated cords have already lost their cavity 

 entirely. Bounded by the mesoderm the intercalated cord as- 

 sumes in cross-section the form of a trapezoid. It is convenient to 

 distinguish here three kinds of the mesoderm-lamellœ, the upper, 

 basal, and the vertical. The upper lamelki {u.l.) is situated along 

 the surface of the disc, the basal (b.L), in the lloor {i.e. in the dia- 

 phragm), and the vertical [u.l.) connects these two lamelhe. 

 When traced inwards, (PI. XV Figs. 6, 7) the intercalated cord 

 becomes thinner and thinner, until it no longer shows in cross- 

 section the form of a trapezoid, but assumes the shape of a tri- 

 angle formed by two vertical and one basal lamella. AVhere the 

 gonosome arises (Fig. 8), the vertical lamella does not reach the 

 upper lamella ; hence the radial canals communicate here with one 

 another and form the upper common cavity of the hydranth. 



