INTESTINE. 79 



distinctness for a short distance behind the gill-slits as a groove on the 

 dorsal wall of the oesophagus ; this has been called the postbranchial canal. 



The pharynx is followed by the oesophagus (or afferent in- 

 testine as it has been called), which extends throughout the 

 hinder part of the branchiogenital region and leads into the 

 hepatic intestine. This structure occupies the anterior part of 

 the abdominal region of the body and is distinguished by the fact 

 that its walls contain green or brown pigment globules. In the 

 Ptychoderidse and in iSchizocardium it gives off the hepatic 

 diverticula already referred to. These are arranged in two 

 dorso-lateral rows, one on each side, and open into the intestine 

 by transverse slits. The boundary between the oesophagus and 

 hepatic intestine is not very sharp, especially when the hepatic 

 diverticula are not present. 



In Glandiseps hacksi there is a kind of siphonal tube or accessory in- 

 testine in the hepatic region on the dorsal side. It leaves the hepatic in- 

 testine at about the middle of its length and joins it again at its hind end. 



Spengelia alba is distinguished by possessing hepatic diverticula which 

 do not cause external sacculations of the body wall. 



In some species the oesophagus and anterior part of the hepatic intestine 

 sends off dorso-laterally short canals which open to the exterior by pores 

 which are placed on each side of the dorsal surface in a line with the branch- 

 ial pores. These pores are in two sets. The anterior set comprises the 

 so-called unpaired intestinal pores. These are placed in the part of the 

 branchiogenital region immediately following the pharynx, i.e. on the 

 anterior part of the oesophagus, and as their name implies are usually 

 unpaired. They are found in Schizocardiumbrasiliense, 13 on one side and 

 16 on the other ; in Glandiceps hacksi 9 altogether, one on the right 

 side and the rest on the left. The posterior set is known as the paired 

 intestinal pores. These are placed at the hind end of the branchiogenital 

 region, or front end of the hepatic, and communicate either with the hind 

 end of the oesophagus or front end of the hepatic intestine. They are 

 found in Schizocardium brasiliense (one pair), Glandiceps hacksi (three 

 pairs), Dolichoglossus kowalevskii (four to six pairs) ; also in D. mere- 

 schkowskii and in Spengelia alba. 



The hepatic intestine passes without any strong line of de- 

 marcation into the intestine proper or efferent intestine which 

 occupies the hinder part of the abdominal region. This section 

 becomes somewhat narrower behind where it forms the rectum 

 which opens outward by the wide terminal anus. 



In most Ptychoderidse a median rod of endoderm is marked off from the 

 ventral wall of the hinder part of the intestine. It occurs as a thickening 

 of the gut wall, or as a tube with an interrupted lumen opening at both 

 ends into the gut, and has been called the pygochord. It lies in what 

 may be called the caudal part of the body and extends back to the anus. 



