1x ALIMENTARY CANAL 259 
is said to be present in connexion with that part of the 
intestine which contains the spiral valve. In Protopterus,' and 
also in Neoceratodus, there is a well-developed ventral mesentery 
in relation with the greater part of the length of the intestine, 
although in the former Dipnoid its continuity is interrupted by 
Fic. 157.—Transverse section through a portion of the wall of the intestine, combined 
from the condition seen in both the higher and the lower Vertebrata, Semi- 
diagrammatic. «a.c, Epithelial cells in the amoeboid state ; b.v, blood-vessels ; c.m, 
circular muscular layer ; g, one of Lieberkiihn’s glands in the higher Vertebrates ; 7.ep, 
intestinal epithelium ; 7, leucocytes ; 1’, leucocytes in the intestinal epithelium ; 7,7, 
lymph follicles; 7.m, longitudinal muscular layer; dym, lymphatic vessels; p, 
visceral layer of the peritoneum ; sm, the submucosa ; v, villi of the higher Verte- 
brates. (From Wiedersheim.) 
one or two vacuities, and in the latter the mesentery is incom- 
plete posteriorly. A ventral mesentery is also present in the 
intestinal region of some of the Muraenidae among Teleosts.° 
Internal to its peritoneal investment the wall of the alimentary 
canal consists in succession from without inwards of (1), a 
1 Newton Parker, Zrans. Roy. Irish Acad. xxx. 1892, p. 140. 
2 Giinther, Phil. Trans. 161, 1871, pp. 542-543. 
3 Owen, Anat. Phys. Vertebrates, London, 1866, i. p. 424. 
