74 



BALANOGLOSSIDA. 



The alimentary canal extends as a straight tube from mouth 

 to anus. The mouth (p. 68) leads into a wide tube which traverses 

 the collar region and is called the buccal cavity. The buccal 

 cavity passes at the junction of collar and trunk into the 

 pharynx in the side walls of which the branchial slits are placed ; 

 this leads in the hinder part of the branchiogenital region into 

 the oesophagus which passes behind into the intestine. The 

 anterior part of the intestine is distinguished as the hepatic 

 intestine from the posterior part which opens by the anus. The 

 part of the intestine next the anus is distinguished as the rectum. 

 The wall of the hepatic part of the intestine contains a greenish 

 or brown pigment, and in the Ptychoderidse and in Sckizocardium 



FIG. 60. Diagrammatic longitudinal- vertical section of Ptychodcru (from MacBride). C col- 

 lar ; Pr proboscis ; Tr trunk. 1 proboscis coelom ; 2 glomerulus ; 3 heart ; 4 pericardium ; 

 5 proboscis pore ; 6 collar coelom ; 7 collar nerve-cord ; 8 dorsal nerve roots of 7 ; 9 dorsal 

 blood-vessel ; 10 dorsal mesentery ; 11 external opening of the branchial sac (not clearly 

 shown), 12 U-shaped internal opening of the same ; 13 ventral blood-vessel ; 14 ventral 

 part (hypobranchial groove) of the branchial region (pharynx) of the alimentary canal: 

 15 dorsal part of the branchial region of the same ; 16 buccal cavity ; 17 mouth ; 18 noto- 

 chord ; 19 cuticular sheath of the same ; 20 ventral pocket of proboscis coelom ; 21 ventral 

 mesentery of proboscis coelom. 



possesses on each side a row of hepatic diverticula which cause 

 the hepatic sacculations of the body wall visible in these genera. 

 The alimentary canal is lined by a more or less columnar epithe- 

 lium and is ciliated throughout. It is attached to the body wall 

 in the dorsal and ventral middle lines by longitudinal mesen- 

 teries ; which however in the adult are deficient in certain parts 

 of the body (see below, pp. 87, 89). 



The buccal cavity gives off from the anterior part of its roof, 

 in the dorsal middle line, a forwardly directed csecal diverticulum 

 (Figs, 60, 64), which, following Bateson, we shall call the noto- 

 chord. The notochord is a tubular structure which extends 

 through the neck of the proboscis and projects into its base. 

 It is divisible into two regions : the narrower neck which lies 



