284 I. IJIMA : HEXACriNELLIDA. I. 



the terminal one. Each such opening leads into a small cavity 

 (PI. XIII, fig. 21 ; cav. hy.) which invariably harbors a hydranth 

 of the commensal Hydrozoa. The cavity serves the part of a 

 hydrotheca to the naked hydranth. Special canals proceeding 

 from it for the reception of the branched cœnosarc can not be 

 perceived. According to Kuma's statement, the tips of the 

 tubercles in the fresh state present a pinkish color, which 

 probably belongs to the Hydrozoa in question. 



There exist on both the stem and the branches all sorts of 

 transitional stages between simple tubercles and such as deserve 

 to be called inceptional branches or twigs. The growth into the 

 latter is evidently initiated by a multiplication of the hydranths 

 and by the formation of new openings for these, and eventually 

 of new tubercles. So long as they are small and simple, the 

 tubercles are made up entirely of the loose, superficial sponge- 

 tissue and can therefore be easily rubbed off. As they progress 

 in their development into branches, they acquire for their support 

 an axial core of parenchyQial strands branching out from the same 

 of the parts on which the developing branch is borne (see the 

 lower end of fig. 20). PI. XII, fig. 2 shows a skeleton in which 

 the superficial loose tissue together with the tuberosities had been 

 entirely scraped off. 



The branches, varying in thickness from less than 1 mm. to 

 oY^. mm., spring out on all sides of the stem, though exhibiting 

 different degrees of development in certain pai'ts as will soon be 

 pointed out. They generally arise from the stem at nearly right 

 angles. When somewhat obliquely inclined, they are directed 

 superiorly about as often as inferiorly. They are usually nearly 

 straight, though I have found many of the branches almost uni- 

 formly curved upwards in onu specimen and downwards in another. 



