NOTE ON A GIGANTIC AURICULARIA. 



35 r 



(fig. 3, hy). As regards the formation of the ring canal, CllUN made 

 a suggestion in the following terms : " Wollte man nun annehmen, 

 dass der langgestreckte Kanal die Anlage des Ambulacralringes 

 abgebe, indem er sich später derart hufeisenförmig krümmt, dass das 

 Hinterende (Taf. III, Fig. 5, à) mit dem links neben dem Mitteldarm 

 gelegenen Vorderende (aiub.) verschmilzt, so könnte man in den 

 rechts (schräg nach vorn) abgehenden Seitenästen die Anlagen der 

 Fühlerkanäle und in den links (schräg nach hinten) gerichteten 

 Seitenästen die jungen Radiärkanäle erblicken." This is not in agree- 

 ment with the facts observed by me. It can be clearly made out in 

 my specimens that the ring canal is formed by enlargement of only 

 the anterior knob-shaped end (indicated amb in Chun's figures), and 

 not by the whole extent, of the thin- walled branching canal (ae) 

 which CHUN took for the " Ambulacralsystem." The main branching 

 part of the canal, I am strongly inclined to think, corresponds to the 

 space discovered in the young of Cucumaria plaiici, C. crocea and 

 some other Holothurids, which was called " anterior enteroccel " t 

 (BURY 1889), " Madreporenblase " (Ludwig '91), or "axial sinus" 

 (MacBkide and SIMPSON 1908). The wall of this canal is ex- 

 tremely thin and can not be perceived except in the living larva-. 

 The hydroccel is a broad flat sac situated on the left side of, and 

 obliquely inclined towards, the hind end of the œsophagus. On the 

 antero-lateral side of the hydroccel, where its wall is thickest, there 

 are observed five or more outbulgings separated by parallel furrows 

 running in dorso-ventral direction. The said outbulgings probably 

 represent the rudiments of tentacular canals and also of some radial 

 canals. In the middle of its dorsal edge the hydroccel communicates 

 with the anterior enteroccel. The pore-canal (pc) and the water-pore 

 (wp) show no difference from those of the Orotavan form ; they are 

 well defined and very conspicuous together with tiie hydroccel. That 

 part of the anterior enteroccel which connects the hydroccel with the 

 proximal end of the pore-canal will probably develop into the stone- 



