1901.] NATURAL SCIENCES OF PIIILADELrBIA. 687 



The lateral areas of sections of the eutire body have beeu care- 

 fully examined, but no indication of any constantly recurring de- 

 pressions could be found in any other region of the body, either 

 anteriorly or posteriorly. Here and there, of course, as in most 

 Nemerteans, are small depressions of the surface due to contrac- 

 tion and shrinkage, but their extent is very limited, and they may 

 occur in any position, dorsal, ventral or lateral. 



Fig. 62 is a cross section of a portion of the body wall through 

 one of the lateral grooves. It shows that the lateral groove, 

 L.G., is a depression both of the body epithelium, Ep., and of 

 the outer longitudinal muscle layer, o.L.M. The epithelial cells 

 in the groove are rather closely crowded together, and the indi- 

 vidual cells are not distinguishable with the magnification used. 

 With a higher magnification, it may be seen that the epithelium is 

 composed of supporting cells, gland cells and interstitial connec- 

 tive tissue cells, just like the rest of the body epithelium. There 

 is no differentiation of the epithelial cells in the groove. Culis 

 gland cells of the blue-staining type, Cu.Gl.^, are present in the 

 outer longitudinal muscle layer around the lateral nerve chord 

 below the groove, and their ducts open between the epithelial 

 cells of the groove. 



The peculiar appearance of the lateral nerve, as shown in fig. 

 62, has already been discussed. 



The question now to be considered is, What are the lateral 

 grooves ? Are they the result of contraction — i.e., artifacts — or 

 are they organs of the body ? 



The question whether the lateral grooves are merely contractions 

 seems to me to be disposed of by the facts of their constant posi- 

 tion, extent and regular occurrence in several individuals. The 

 alternative, then, is that they are paired organs of the body ; but 

 with what function ? 



When these grooves were first observed, I believed that they 

 were sense pits, comparable to the lateral sense organs ("Seiten- 

 organe") of the Protonemerteans, and I hoped that further study, 

 both upon living worms and sections, would demonstrate the pres- 

 ence of sensory cells and possibly of nerves. 



The careful study of sections has not revealed any differentia- 

 tions of the epithelial cells of the lateral groove, although no 

 especial nerve technique, such as the Golgi or methylen blue 



