550 n. C. PUNNETT. 



so orientated that the muscle crosses are dorsal and ventral, 

 the nerves are then lateral in position. There is no continuous 

 nervous layer such as occurs in the majority of the group. 



The alimentary canal presents no features of special 

 interest in its structure. The oesophageal epithelium contains 

 unicellular glands, and unicellular glands also form a layer 

 round it. In the intestinal region the gut pockets are deep, 

 and there is a well-mai^ked ventral gutter. The gut pockets 

 are continued to the anus, which is a comparatively large 

 opening at the posterior end of the body on the dorsal 

 surface just in front of the caudal appendage. For the last 

 millimetre or so the alimentary canal and its pockets are 

 devoid of gland cells. The whole canal is richly ciliated 

 throughout. 



The vascular system (fig. 11) in the snout consists of a 

 large lacuna which divides just in front of the brain. At the 

 level of the brain commissures these unite ventrally, and then 

 again divide into two lateral and a median dorsal vessel. The 

 lateral vessels form lacunae round the cerebral organ. At this 

 level they again communicate by the buccal commissure, 

 though no buccal vessels are formed. Behind the cerebral 

 organ the lateral vessels pass backwards to the oesophagus, 

 where they form the (^esophageal lacuDte characteristic of the 

 order. This lacunar network is co-extensive with the excretory 

 tubules. As soon as the tubules cease the oesophageal lacunae 

 are gathered into a very lai'ge lacuna on either side (fig. 1). 

 This condition lasts until just after the level of the excretory 

 pore, when the lacunae become constricted and suri-ounded with 

 the peculiar pai'enchymatous tissue found in the rest of the 

 Heteronemertini. The median dorsal vessel runs in the pro- 

 boscis sheath until the level of the excretory pore,^ when it 

 emerges and becomes surrounded by parenchymatous tissue 

 like the lateral vessels. In the intestinal region the lateral 



* In a previous paper I have already drawu atteiilion to tlie curious fact 

 that the dorsal vessel almost invariably leaves the proboscis sheath at the 

 level of the hind end of the excretory system, whatever may be the extent 

 of the latter. ('Quart. Journ. Micr. Sci,,' vol. 44, p. 136.) 



