TWO NEW BRITISH NEMERTEANS. 549 



is the thickest, and this relation obtains throughout the body. 

 In the posterior oesophageal region the alimentary canal is 

 completely surrounded by a layer of longitudinal muscles, 

 separated off from the inner longitudinal layer. The inner 

 longitudinal layer also separates the circular layer and the 

 proboscis sheatli. Dorso- ventral fibres occur in the posterior 

 oesophageal region as well as between the intestinal pouches. 

 The last are, however, but poorly developed. There are a 

 few horizontal fibres above the mouth. The outer longi- 

 tudinal layer is feeble in the oesophageal region, owing 

 possibly to the great development of the cutis glands. It 

 becomes more strongly marked in the anterior part of the 

 intestinal region, but entirely disappears towards the pos- 

 terior end of the auimal. The caudal appendage contains 

 prolongations of the circular and internal longitudinal layers 

 (fig. 8). 



The proboscis sheath possesses an outer circular and an 

 inner longitudinal layer of muscles. It exteuds throughout 

 the length of the animal, though it does not reach into the 

 caudal appendage. In the oesophageal region occur divei'- 

 ticula (figs. 1 and 11, rhc. p.) from the proboscis sheath 

 in which the muscle layers are absent. These diverticula 

 are closely embraced by the lateral vascular lacunae in this 

 region. They are crowded with large rhynchoccelomic cor- 

 puscles, which are oval in shape and greatly flattened (fig. 9). 

 Each contains a nucleus in which the chromatin is arranged 

 in four small circular masses, all connected by a more or less 

 circular thread. Similar corpuscles are to be found in the 

 cavity of rhynchocoelom, and also in the vascular lacunee in 

 this region. The proboscis is not long. In its middle 

 portion it is composed (when retracted) of an outer longi- 

 tudinal muscle layer directly beneath the rhynchocoelomic 

 epithelium, containing two muscle crosses (fig. 4) formed by 

 fibres from the thinner circular layer directly beneath it. 

 Beneath this again is the high and glandular proboscis 

 epithelium. Just inside the circular muscle layer are several 

 nerves on either sidej that is to say, if the proboscis is 



