1901.] 



NATURAL SCIENCES OP PHILADELPHIA. 



665 



It is seen here that the most 

 anterior part of the head is 

 entirely free from cutis gland cells, 

 but that about 0.5 mm. behind 

 the tip the blue-staining cells 

 are very abundant, distributed 

 uniformly on all surfaces of 

 the body. The red -staining 

 cells occur in small numbers 

 and ax'e mostly on the ventral 

 surface; they are of the finely 

 granular variety. From the 

 mouth back to some distance be- 

 hind the nephridia the blue- 

 staining cells are quite numer- 

 ous, interspersed with the red- 

 staining cells. Just behind the 

 great rhynchoccelomic expansion, 

 where the circular muscle of the 

 body wall is considerably thick- 

 ened, comes a region that might 

 properly be called a glandular 

 zone, Gl.Z., owing to the enorm- 

 ous increase in the number of 

 the cutis gland cells. The 

 whole outer longitudinal muscle 

 layer is so crowded with them 

 that in a cross section the muscle 

 fibres seem nearly obliterated. 

 The cells increase also in size, 

 or perhaps are more distended 

 with secretion. The blue-stain- 

 ing cells are more abundant 

 than the red. This zone ex- 

 tends backward for about 3 mm. , 

 then suddenly ends, just in front 

 of the two lateral grooves, L. G. 



In the lateral groove region, fig. 

 23, Ca.Gl.,, Cu.Gl.,, the blue 

 cells are confined to two tracts, one 

 on eacn side of the body, above 

 the lateral nerves. The red-stain- 

 ing cells are in four tracts, dorsal 



LG 



Diagram 1. — The head and part of 

 the body of ZygeupoUa, illustrating 

 the distribution of the cutis gland 

 cells. — The outline of the alimen- 

 tary tract is given as a means of 

 orientation. Gl.■^, red-staining cu- 

 tis gland cell ; Gl..^, blue-staining 

 cutis gland cell ; Gl.Z., glandular 

 zone; L.G., lateral groove; M., 

 mouth. 



