NEEVOUS SYSTEM OF ANTEDON EOSACEUS. 511 



cords is rather complicated; but it is necessary to describe it in 

 some detail, as it is with these parts that we shall be specially 

 concerned later on. 



The central capsule is lodged as we have seen in the hollow 

 of the centrodorsal plate and is covered on its ventral surface 

 by the rosette ; it forms a complete investment to the cham- 

 bered organ (fig. 1) excepting where it is perforated by the 

 central plexus in the middle of the ventral surface. The dorsal 

 and lateral walls are, as shown in the figure, thicker than the 

 ventral. 



From the dorsal surface are given off processes to the cirri 

 (fig. 1, e) each of which is traversed down its centre by a vessel 

 derived from the central plexus. 



From the margin of the central capsule arise five short inter- 

 radial processes (figs. 1 and 3), which passing ventralwards and 

 slightly outwards bifurcate into right and left branches 

 between the centrodorsal plate and the First Radials. These 

 branches diverging from one another enter the substance of the 

 First Radials, and then unite in pairs, the right branch of one 

 interradial stem uniting with the left branch of the one next to 

 it, to form five stout radial nerves (fig. 3) which run outwards 

 in the substance of the First and Second Radials. On reaching 

 the boundary line between the Second and Third Radials each of 

 these radial cords divides into two branches right and left, which, 

 traversing the Third Radial, enter the right and left arms respec- 

 tively of the pair, along which they pass as the axial cords 

 (figs. 1, 2, 3 a), in the substance of the brachials or calcareous 

 segments of the arms. 



Besides the connections described above there are certain 

 others which must be noticed. A pentagonal commissure 

 (fig. 3} connects all the branches together immediately after 

 they have entered the First Radial. There is also a further 

 connection in each Third Radial between the branches into 

 which the radial cord divides to supply the two arms of the 

 pair ; this connection, as shown in fig. 3, consists of a trans- 

 verse commissural band of fibres, and a chiasma formed by two 

 obliquely placed bands which cross one another and furnish 



VOL. XXIV. NEW SER. M M 



