130 BULLETIN OF THE 



of the tentacles also, are in free comrnuTiication with the fluids of the 

 conmion body cavity. As Figure 51, Plato V., shows, the posterior ends 

 (if tiie ling canals open into a pair of cavities which are the bases of the 

 Idplidjihoric ])ockets, and liy a coni])avison of Figures G1-G3, cxri. crc, am. 

 or.', i'iate \' 1 1., it will become ajiparent that they each beconic CDnilticnt 

 with a I'lirruw which ])asses up the lophdjihore arm, and from which tlie 

 outer lophophoric row of tentacles is developed. Further, by a com- 

 parison of can. or.", cati. crc.'", in Figures G1-G3, Plate A'll. (dcxtro- 

 sinistral vertical sections), and Figure f)!), Plate V. (horizontal section, 

 coinj)arc also Fig. 52, a sagittal section), it will be seen that from 

 the tip of the lophoj)horic arm a groove (can. crc") passes down iipon 

 the side opposite to the ascending groove ((•««. crc.'), and, reaching the 

 base, fm-iis abiaiptly anteriorly {can. crc.'". Fig. 50), and finally, in 

 .a later stage, becomes confluent with its fellow of the opj)osite side 

 in the median plane, just behind the e])istome and above the l)rain. 

 It w(jul(l be quite unnecessary for me to give figures showing the 

 course of this supragangl ionic canal (cf f'^ig. 52, Plate V.). It has 

 long been recognized, and is shown in Kraejielin's ('87) Figure GG, 

 Taf. II. This is probably what Vcrworn ('87, pp. 114, 115, Figs. 20 a, 

 20 b, Taf Xll.) has described as a "segmental organ." Braem ('89'', 

 p. G71)) has given to it the name " Gabelkanal." The " Piingkanal " of 

 Nitsche is, then, to my mind, merely the circumoral portion of a groove 

 which is elsewhere unclosed to form a proj)er canal and which lies at 

 the base of all tentacles. My reason for avoiding another term for the 

 unenclosed portion of the "canal" is, that I regard the whole as mor- 

 phologically equivalent to the ring canal of Gynmohemata, which is 

 said to bo closed throughout. 



2. Development of the Lophojihore. — The early stages in the forma- 

 tion of this organ are well known, both from the descriptions of Nitsche 

 ('75, pp. 357, 358) and the earlier ones of Allman and others. 



I have already (page 114) shown how the cavities of the lophophoric 

 pockets become confluent between the rectum and ganglion, and how 

 their opposed walls, formerly passing over into each other through the 

 floor of the brain, are now anteriorly continuous by means of the new 

 floor of the atrium, and posteriorly are fused together. 



The union of the inner layers of the two opposed walls of the lopho- 

 phore arms (Plate Y. Fig. 44, loj^h.') continues, however, for some dis- 

 tance above the floor of the atrium, up to within a short distance of the 

 tips of the young arms (Plate VIT. Figs. Gl, G2, lojth.'). As the arms 

 grow longer, the relative extent of their free and fused portions remains 



