342 . A. T. MASTEEMAN. 



springs and for some distance on the dorsal surface of the 

 buccal disc." He also noticed that the general arrangement 

 was similar to that of Phoronis. Harmer (1) showed further 

 that nervous branches passed up the dorsal sides of the arms. 

 As will be seen by inspection of the accompanying figures, in 

 which the nervous system is coloured yellow, my sections 

 confirm the previous results, and make further statements 

 possible. The main nerve-ganglion (PI. 23, iig. 3, w. g.) lies 

 over the subneural blood-sinus [s. n. s.), which is a haemal 

 space immediately between the mesodermal wall of the pre- 

 oral body-cavity (epistomial) and those of the collar cavities. 

 In other words, it is in identically the same position as the 

 nerve-ganglion of Actinotrocha. On the walls of the sub- 

 neural sinus arise the inner ends of the "proboscis pores'' 

 (or canals) [p- p-), which then lead forwards and upwards on 

 either side of the ganglion to the exterior (see PI. 23, figs. 2 

 and S,p.p.). This arrangement of proboscis canals, subneural 

 sinus, and ganglion is precisely similar to that of Actino- 

 trocha. 



Traced backwards (fig. 4), the main ganglion gives off the 

 thick lateral branches to the arms, whilst further back it con- 

 tinues its course, overlying the thin dorsal blood-sinus between 

 the two collar cavities (figs. 5 — 8). By the time fig. 9 is 

 reached (cf. PL 24, fig. 13) the pharynx, or more possibly the 

 basal part of the subneural gland, comes to lie close under 

 the nervous mass, which then divides into two lateral nerves 

 (fig. 12, /. n.). These give off a post-oral ring at the posterior 

 edge of the collar region (PI. 25, fig. 15), which becomes 

 lost ventrally in a mass of nerve-fibres, scattered over 

 the inner surface of the ectodermal layer of the post-oral 

 lamella (fig. 13). The lateral nerves are then continued as a 

 pair of rather broad nerve-tracts, lying laterally in a position 

 similar to those of Phoronis. 



Anteriorly, the ganglion is continued as a mass of fibres 

 along the upper surface of the epistome, in the mid -dorsal line 

 and somewhat to each side of it (figs. 1, 13, 14), round the 

 apex, and then unites with a very broad flat ring which lies at 



