552 H. LYSTER JAMESON, 



in the body cavity dorsal to the fore-gut and segmental organs. 

 Naturally the relative positions of the windings depend largely on the 

 degree of distension and contraction of the parts. 



The walls of the intestine seem to be of very uniform thickness 

 throughout, though possibly in the last part, where only the ciliated groove 

 is present, they are a little more muscular. Variations in the calibre 

 of the intestine and in the thickness of its walls are apparently due 

 to the contents, of which fact a comparison of numerous individuals 

 has convinced me. We have here a remarkable instance of one of 

 those long, thin-walled, plastic intestines which usually characterize 

 sand-eating Invertebrates. On comparing any two examples we find 

 frequently that the part which in one is a comparatively thickwalled 

 narrow tube, is, in another individual, distended to form a great 

 thin-walled transparent sack through which we can observe multitudes 

 of food balls. A dorsal mesentery supports the intestine throughout 

 its entire length. The ciliated groove with its derivative, the collateral 

 intestine, is ventral in position. This can be determined at the two 

 ends of the groove, which, at the pre-intestinal constriction arises on 

 the opposite side to the^ dorsal blood vessel (Fig. 12 p) while po- 

 steriorly it ends at the coecum which is ventral in position and, 

 indeed, supported by the ventral mesentery (Fig. 11 coe). Further, 

 throughout the entire length of the intestine the dorsal mesentery and 

 the ciliated groove are on opposite sides. 



The collateral intestine arises suddenly from the groove, its point 

 of origin being often a little more inflated than the remainder 

 (Fig. 12 c.i); but this inflation is not always present. It is of very 

 uniform diameter throughout and is always closely apposed to the in- 

 testine, never being separated from it by a space spanned by mesenteries 

 as in some Capitellids. 



When the part of the digestive tube in which the collateral in- 

 testine arises is removed, and the dorsal wall carefully cut away so 

 as to expose the inner aspect of the ventral wall, and the preparation 

 cleared with oil of cloves, we see that the ciliated groove actually 

 goes over into the collateral intestine, the latter opening out into the 

 alimentary canal by a circular orifice (o), which is bounded posteriorly 

 by a thickened fold formed by the fusion of the walls of the ciliated 

 groove (Fig. 21 c.gr). 



The shallow groove (s. gr) which is seen running backwards from this 

 point accompanying the collateral intestine, cannot therefore be referred 



