Notes on the Adult Anatomy of Solaster endeca. 179 



that blank in the floor of the central chamber which was referred to above 

 as forming the commencement of the stone canal. 



This communication in a young Solaster endeca, according to Goto (7), was 

 through a lateral opening on the dextral side of the commencement of the 

 canal. Evidently its lower lip has grown up, so that the margin of the open- 

 ing is now horizontal instead of vertical, and at the same time the aboral end 

 of the axial sinus has become divided into a branching set of spaces, all com- 

 municating directly or indirectly with the central chamber described above. 

 The central chamber itself represents that part of the axial sinus which, in 



Fig. 5. 



Diagram to illustrate in vertical section the relation of pore canals, stone canal axial 

 sinus, etc., in a large adult Solaster endeca. The branching of the pore canals has 

 been greatly simplified. (Lettering as in Figs. 1 to 4.) 



early stages, lay adjacent to the laterally placed opening of the stone canal. 

 What has been described by various authors as the ampulla of the stone 

 canal seems to correspond with this chamber in the adult condition (or earlier 

 with the more open dextral end of the axial sinus). In this view the term 

 ampulla of stone canal is, strictly speaking, a misnomer, and should be 

 replaced by ampullary part of axial sinus or some similar name. 



In the adult S. endeca, the position may be summed up as follows : — (1) 

 The central set of pore canals open into collecting trunks leading into the 

 ampullary part of the axial sinus which leads directly into the stone canal ; 

 (2) the marginal set of pore canals form collecting trunks which lead into 

 the upper end of the axial sinus, and also communicate freely with the 

 ampullary chamber; (3) strictly speaking, none of the pore canals of the 

 madreporite should be described as opening into the stone canal. 



