462 PBOP. A. DEIfDT OK SOME POINTS IK 



circumanal ampuUse* were in a state o£ dilatation wliile the 

 tentacles themselves were in a state of contraction. It will also' 

 be seen from figs. 5 and 11 that the circumanal ampullae contain 

 a large number of nucleated corpuscles {corp.), which shows that 

 they must have been filled with liquid at the time of the 

 animal's death. In the contracted anal tentacles themselves 

 the ambulacral vessels appear as narrow cavities surrounded by 

 an inner epithelium, outside which lies a layer of very slender 

 longitudinal muscle-fibres difiicult to recognize, and then a very 

 delicate outer ej)ithelium (fig. 12). 



I have not been able to trace the radial blood-sinus or lacuna 

 beyond the point where the ambulacral vessel gives of£ its lateral 

 branches. Grerould, however, in the case of Caudina arenata,. 

 states that the radial blood-lacunae communicate with a circular 

 lacuna surrounding the anal opening. He also figures f what 

 appears to be an immense dilatation of the radial blood-lacuna^ 

 occupying almost the entire cavity of the anal papilla or terminal 

 tentacle. 



TJp to the point where the radial ambulacral vessel gives off 

 its branches to the anal tentacles, the radial nerve maintains itS' 

 typical structure, consisting of an inner and an outer band 

 accompanied respectively by the hyponeural and epineural canals 

 (fig. 12). Shortly after the ambulacral vessel divides, however, 

 the inner nerve-band dies out, leaving only the outer band, 

 which also divides into branches, one of which accompanies each 

 branch of the ambulacral vessel into an anal tentacle (figs. 11,. 

 12). The epineural canal (fig. 11, <?/>.) also divides, and its branches 

 accompany the corresponding nerves for some distance, but 

 afterwards disappear. At first also each branch of the ambulacral 

 vessel, where it swells out to form an ampullary organ, is accom- 

 panied on its outer aspect by a distinct canal, lying outside the 

 layer of longitudinal muscle-fibres and inside the nerve (fig. 11), 

 Whether these canals are derived by a branching of the hypo- 

 neural canal or by sudden enlargement and branching of the 

 radial blood-sinus, I have been unable to determine owing to 



* As I am not aware that ampullary organs have hitherto been described in 

 this position, I have ventured to distinguish them by the term " circumanal 

 ampuUse" from the numerous other ampullae vrhich occur in the body of a 

 Holothurian. 



t Loc. cit. ijlate iv. fig. 50. 



