44 W. G. RIDEWOOD. 



behind the level of the mouth. Along each sicte of the pharynx a part of the 

 wall is composed of pale-staining vacuolated cells the pleurochord. The 

 pleurochord has a groove which runs lengthwise along the lateral wall of the 

 pharynx and opens into the gill-slit anteriorly. The pleurochordal cells surround 

 the gill-slit. 



The pharynx narrows very abruptly behind, and leads into the next portion 

 (stomach) by a very small aperture. The stomach is in no case dilated ; it is 

 continued forwards as a caecum, of oval section and with thick walls, which lies 

 between the intestine and the two gonads (see text-fig. 14, p. 39); and it leads at 

 its posterior end into the intestine, which passes first ventrally, then posteriorly, then 

 dorsally, and finally forwards, and opens by an anus at the front end of the 

 body. In the specimens preserved in formalin the intestinal wall is pale green. 



Much discussion has centred around the structures mentioned above as the 

 notochord and pleurochords. The pleurochords were so termed by Masterman 

 (22, p. 353, footnote), who, since the year 1896 (20, p. 64) is disinclined to 

 recognise any homology existing between the median pharyngeal diverticulum 

 above referred to as the notochord, and the notochord of the Vertebrata. He 

 at first denied that any homology exists between the median diverticulum of 

 Cephalodiscus and the Eicheldarm of Balanoglossus, but he has since ceded the point 

 (28, p. 723) and admits an homology between the median diverticulum of 

 Cephalodiscus and the vermiform process of the Eicheldarm. He homologises the 

 former structure with the subneural gland of Tunicates (22, 23, 27, 28), and 

 now regards the Eicheldarm of Balanoglossus as a subneural gland also 

 (28, pp. 723 and 724). 



Willey has shown that the complete stomochord or anterior diverticulum 

 with vacuolated walls occurring in the Enteropneusta exhibits strongly marked 

 regional differentiation (34, p. 235, fig. 3), and he homologises Masterman's 

 pleurochords of Cephalodiscus and Actinotrocha with the lateral pouches of the 

 stomochord, and the median ventral diverticulum, arising from the anterior end 

 of the intestine and underlying the oesophagus, described in Actinotrocha by 

 Roule (Comptes Rendus, cxxvii., 1898, pp. 633-636, and Ann. Sci. Nat. Zool., 

 xi., 1900; see also Ikeda, Journ. Coll. Sci. Imp. Univ. Tokyo, xiii., 1901, 

 pp. 555-556), with the ventral caecum of the stomochord (34, p. 237). He agrees 

 with Harmer (7, p. 342) that the notochord of Cephalodiscus (subneural gland 

 of Masterman) is the equivalent of the vermiform process of the stomochord * of 

 the Enteropneusta, but in this connection it is to be noted that Harmer has 

 recently stated (10, p. 65) that he regards the notochord of Cephalodiscus as 

 equivalent not with the vermiform process alone, but with the entire Eicheldarm. 



Willey shows further that the hinder region of the gut of the Enteropneusta 

 may develope in its ventral wall a skeletal vacuolated structure, the pygochord 

 (34, p. 234). The pygochord Masterman (Quart. Journ. Micr. Sci., xliii, 1900, 



