328 ME. A. E. SHIPLEY ON THE GENUS SIPUNCULtTS. [Apr, 18, 



an irregular edge. The extent to which it is developed, however, 

 varies remarkably ; it may form but a simple ring (Plate XXVI. 

 fig. 6) as in S. tessellatus, or it may be bent in, thus forming a 

 double horse-shoe, open in the middle line dorsally, or finally it 

 may be again bent out as shown in Plate XXVI. fig. 5. This 

 is the most extreme case I have as yet met with in the arrange- 

 ment of the ciliated membrane round the mouths of members of 

 this genus. 



In Sipuncuhis indicus the head is followed by a short neck, from 

 ^ to I an inch long, which is covered by a number of flattened 

 scale-like papillae, which are bent back, and lie over one another 

 like tiles on a roof (Plate XXA^. figs. 4 & 8). Behind the head the 

 body is conspicuously ringed. 



The skin presents the usual layers of tissue. Within it is 

 clothed by a layer of peritoneal epithelium ; then come the longi- 

 tudinal bundles of muscle-fibres, 38 to 40 in number (Plate XXV. 

 fig. 2, and Plate XXVI. fig. 8), but decreasing posteriorly by the 

 fusion of neighbouring bundles. At the extreme hindermost end 

 the bundles fuse into a ring, and in this region the cuticle is 

 thickened and hardened. The circular muscles which lie outside 

 the longitudinal are very strongly marked ; several of them corre- 

 spond with each of the rings which are so conspicuous on the body. 

 Neither in the body nor in the neck do they ever fuse into a con- 

 tinuous sheet. Outside the circular muscle layer is a layer of 

 connective tissue, which is limited externally by a columnar tailed 

 epithelium, the epidermis ; outside this is a more or less thick 

 coating of cuticle. The connective tissue is a gelatinous-looking 

 tissue with cells scattered through it : prolongations of the body- 

 cavity make their way between the bundles of muscles into this 

 layer and in the region of the neck extend into the scale-hke 

 processes (Plate XXVI. fig. 8) ; these prolongations are seen in the 

 sections to be circular in outline, and to be lined with a layer of 

 peritoneal epithelium; they contain ccelomic fluid, which doubtless 

 serves to nourish the various parts of the skin. 



The papillae which are so characteristic of the skin of Sipunculids 

 are especially common in the scales of the neck of this species. 

 They are not indeed real papillae, as even their mouths do not 

 project above the ordinary level of the skin. They consist of two 

 or three enormously enlarged cells, presumably epidermal in origin, 

 which are crowded with deeply staining granules ; these are appa- 

 rently poured out from the apices of the cells which are aggre- 

 gated together near the mouth of the papilla. The cutis is much 

 thickened in the region of the neck and forms the substance of 

 the scale-like projections ; over the rest of the body it is thinner, 

 and in places corresponding with the grooves between the rings it 

 disappears almost entirely. It is covered by a uniformly thick 

 cuticle, and numerous papilla are scattered through it, though 

 they are not so abundant as in the neck. The scale-like projections 

 on the neck seem to be characteristic of the genus Sipumndus ; 

 no traces of hooks or of the extensile collar, described in Phymosoma, 



