GEROULD: CAUDINA. 141 
connection, and the outer extremity is often exceedingly slender, 
especially when the epineural space is filled with fluid and the 
fibers are consequently stretched. Other nuclei of the covering 
epithelium appear to be connected each with two processes, one 
extending, like the ordinary supporting fibers, inward through 
the outer nerve, and the other, outward across the epineural space. 
Inner band.—The inner band, as in other holothurians, is 
composed of the same sorts of cellular elements as the outer band. 
The nuclei of the covering epithelium send outward processes 
which abut against the connective-tissue partition. I have not 
observed in Caudina processes extending in the opposite direction, 
across the hyponeural canal, such as are shown in Cuénot’s figures 
of Synapta (Planche 28, fig. 48). 
Connective-tissue partition.— An extremely thin layer of connec- 
tive tissue separates the outer from the inner nerve band in Caudina. 
It is composed of fibers which arise from the connective-tissue layer 
on either side of the radial nerve, and at intervals contains nuclei. 
But it is so thin in places that one is not surprised at Hamann’s 
denying its existence. According to this author previous observers 
had been deceived by an optical illusion. Although the connective- 
tissue partition was also overlooked by Jourdan, who in fact did 
not recognize that the radial nerve is made up of an outer and an 
inner band, it has been described by Semper, Teuscher, Semon, and 
Hérouard in Synaptidae, Holothuriidae, and Cucumariidae. 
ce. Neural Canals, 
Hyponeural\ canals.— The existence of five radial neural canals 
lying immediately below the five radial nerves, first made known by 
Semper (68) and Greeff (72), has been noted by Teuscher (’76), 
Théel (82), Semon (’83), Hamann (’84), Hérouard (’89), Ludwig 
und Barthels (’91), and others, so that their presence has been satis- 
factorily demonstrated throughout the whole group of Holothuroidea. 
The anterior ends of these canals were regarded by Semper as termi- 
nating blindly behind the nerve ring. Hérouard also has described 
them in the Cucumariidae as ending blindly at a point immediately 
behind the nerve ring, adjacent to the peripharyngeal space. In 
1I1t seems to me best to abandon the name pseudohaemal yessel, which Ludwig has given 
to this canal in deference to the improbable idea of earlier investigators that it functions 
as a blood vessel, and to adopt a name suggested by its position. 
