PLYiMOUTH NEMERTEANS. 421 



cutis glands are situated not quite half-way between the outer bodywall 

 and the circular muscle layer, laterally at a third of that distance only. 

 The circular muscle layer is separated from the outer longitudinal by 

 a thick nervous layer. Diagonal muscle fibres are absent. The circular 

 muscle layer is rather feebly developed, and has twice the thickness of 

 the epithelium, while the inner longitudinal muscle layer is twice to 

 three times as thick as the circular layer in the oesophageal region. 

 Longitudinal muscle fibres are not present between the oesophagus and 

 proboscis sheath. 



The gonads alternate regularly with the intestinal caeca ; the genital 

 pores are situated above the proboscis sheath. In the intestinal region 

 the outer longitudinal and circular muscle layers are very much 

 reduced. This is especially the case with the outer longitudinal muscle 

 fibres which form a layer of the same thickness as the cutis glands 

 dorsally and ventrally, so that the latter reach the circular muscle 

 layer; laterally, however, the layer of longitudinal fibres is thicker. 

 The circular muscle layer is as thick as the epithelium, but the inner 

 longitudinal muscle layer, which is five to six times as thick as the 

 circular, has the same breadth as in the oesophageal region. 



On the 1st of June part of a jSTemertine was collected in dredging 

 materials from the New Grounds. It turned out to be the posterior 

 part of a very thin (1 mm.) nemertine, completely white, and long in 

 comparison with the uniform breadth. The head failed, but an appen- 

 dix was present. The structure of the body-wall reveals the charac- 

 teristics of a Heteronemertean, as the outer longitudinal muscle layer 

 is present. As with all the layers of the body-wall, this longitudinal 

 muscle coat is very much reduced in size when compared with other 

 nemertines. There are no traces of a cutis nor of any clusters of 

 composite gland cells. Epithelium and outer longitudinal muscular 

 coat have about the same breadth and are separated by the thin base- 

 ment membrane only. The epithelial cells constitute a single layer. 

 The circular and inner longitudinal muscle layers together have but 

 one-third of the thickness of the outer muscular coat. They have 

 about the same breadth. The longitudinal muscle fibres surround the 

 wide enteron and the proboscis sheath, which ends just before the 

 point where the tail is attached. The intestinal pouches are very 

 shallow, and I have not been able to discern any septa. The gonads 

 alternate with the intestinal pouches, or perhaps they are the cause of 

 the appearance of these unreal diverticula. The position of the lateral 

 nerve cords is the usual lateral situation. I have not been able to 

 detect a median dorsal blood-vessel. 



