44 W. G. RIDEWOOD. 
behind the level of the mouth. Along each side 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 KHicheldarm 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, exxvii., 1898, pp. 633-636, and Ann. Sci. Nat. Zool., 
x1, 1900; see also Ikeda, Journ. Coll. Sci. Imp. Univ. Tokyo, xiii, 1901, 
pp. 555-556), with the ventral caecum of the stomochord (84, 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 Hicheldarm. 
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 
(84, p. 2384). The pygochord Masterman (Quart. Journ. Micr. Sci., xliii, 1900, 
