252 M. MIYAJIMA : 



Summary. 



1. The most striking feature in our specimen is its strongly 

 expressed bilateral symmetry as shown by the excentric attach- 

 ment of the hydranth to the hydrocaulus and by an interrup- 

 tion of the circles of the gonosomes, radial canals, and marginal 

 tentacles at the lower edge of the disc. Those who have read 

 the above account will, I think, agree with nie in thinking that 

 this bilateral symmetry is due, not to the primitive state of the 

 body-organization, but rather to its elaboration and specialization. 

 We must therefore regard this remarkable case of bilateral 

 symmetry in a hydriform person as very different from that ex- 

 pressed for instance in the planoblastof Corymorpha and Dicoryne, 

 which is but temporary and occurs only at a certain period of 

 development, or from the biradial symmetry as expressed in a 

 few genera like Ilonobrachium and Lav by a reduction in the 

 number of tentacles. 



2. The hydranth-cavity is divided into two parts, of which 

 the upper is in its outer part again divided into many radial 

 canals visible even on the surface of the disc. That remarkable 

 structure is not, however, peculiar to our specimen. For 

 example, the hydranth-cavity of Tubularia is divided similarly 

 into two parts by a peculiar ring-shaped formation'^' observed by 

 several authors. In Tubularia the lower cavity is narrower than 

 the upper, so that the former forms a slender canal in the middle 

 of the " Wulst." Gosta Grönberg (*98) described in the hydranth 

 of Tubularia indivisa slender endoderm-canals which are the same 

 in number to the proximal (marginal) tentacles and situated 

 between every two tentacle-bases, running obliquely from the cora- 



*0. Hamann ('82) described that formation as " aboral Wulst," G. Grönberz ('98) as 

 " Mesoderm-wulst." 



