NIDAMENTAL TISSUES 



481 



di.tu 



see. 



more exact, they form two longitudinal, lateral bands just inside the 

 longitudinal musculature of the body wall. The cells are enormous 

 in size and very roughly 

 cubical in shape. They 

 lie with what must be 

 considered their proxi- 

 mal end against the lon- 

 gitudinal muscle, and, 

 although they are 

 packed very closely in 

 the layer, there is al- 

 ways a space between 

 them for the access of 

 blood or coelomic fluid. 

 A fine, thin connective 

 tissue with small, 

 highly differentiated 

 cells surrounds the cell 

 body (Fig. 452). 



The nucleus lies 

 somewhat proximal, 



. . 1 10.452. Gland cell from leech, Ptstcola. sec., secreted ma- 



and IS Very irregular in terialsin various stages of elaboration; ncl., nucleolus; nu., 



shape. It is drawn OUt nucleus; cyt.ch., cytoplasmic channels containing and deliv- 



, . . ering the secretion granules to the large distal vacuole; 



at a number OI points di.tu., discharging tubes of this and two other cells. 



on its surface into 



irregular and thin, pointed processes. The chromatin appears as a 

 large number of granules, and there are evidently other bodies in it 

 an achromatic nucleolus and some roughly rod-like and pointed chro- 

 matin bodies. 



The cytoplasm is of most interest. Proximally, it is rather more 

 homogeneous, but, distally, in the cell body its place is almost entirely 

 taken by the great secretion vacuole. Reaching back from this vacuole 

 are a series of branching channels or trophospongia, and in the cytoplasm 

 which borders on the channels can be seen secretion granules in all 

 stages of formation. When completed, these granules are discharged 

 into the channels and carried down into the large secretion chamber or 

 vacuole. 



This vacuole is produced distally into a long tube, which runs, together 

 with a group of similar tubes from other cells of this kind, anteriorly to 

 a region near the head, where all these tubes penetrate the body-wall 

 tissues, and end externally between the columnar epithelium cells of 

 the epidermis. The secretion is mucin, and although the cells have been 

 pointed out as excretory cells, there is no doubt that they are mucous 



21 



