356 



HISTOLOGY 



mass of these cells. They are tall cells with narrow bases and slightly 

 expanded rounded ends. The cells taken from near the typhlasole 

 measure one hundred microns or more in 

 height. The cytoplasm is highly alveolar; in 

 the distal part of the cell it is the denser. 

 Many angular granules of chloragogen are 

 usually held in the cytoplasm. The nuclei are 

 small oval bodies lying near the middle of the 

 cells. Each bears a single nucleolus (Fig. 322). 

 The calcium phosphate cells of Mesodon are 

 large, more or less conical cells, with their bases 

 applied to the membrana propria, or basement 

 membrane, of the epithelium. Their apices 

 always communicate with the lumen of the 

 hepato-pancreatic gland. From apex to base 

 they measure thirty to thirty-five microns. The 

 cells are isolated and surrounded on all sides 

 by the hepato-pancreatic cells (Fig. 323). 



The ureter and bladder serve chiefly as con- 

 ducting and retaining structures. Because of 

 this function their epithelium is compact and 

 stratified. The basal layers of cells in these retaining epithelia tend to 

 be columnar. These support a superficial layer of flattened cells which 

 lie parallel to the surface of the bladder wall. The cytoplasm of the cells 

 is dense. The nuclei are rounded and centrally placed (Fig. 324). 



Beneath the epithelium in both the ureter and bladder is a connective 

 tissue, tunica propria, supplied with scattered elastic fibers, lymphatics, 

 and blood vessels. In both the ureter and bladder there is developed 

 an outer coat, tunica mus- 

 cularis. This also has a 

 connective-tissue frame- 

 work in which smooth 

 muscle fibers are distrib- 

 uted in one, two, or three 

 layers. 



Technic. We have 

 here to do with a very 

 easy tissue to cut and 



FIG. 322. Several chlora- 

 gogen cells from around the 

 intestine of the earthworm. 

 X 650. 



FIG. 323. Cells from the digestive gland of Mesodon 

 (Helix), cal.ph.c., calcium phosphate cell. Others are 

 hepato-pancreatic cells, b.m., basement membrane, on 

 which lies a narrow connective-tissue nucleus. X 970. 



stain by the ordinary 



methods. Sometimes the 



vertebrate kidney, as in 



the mammals, and in Petromyzon, will prove refractory and get brittle, 



but a second attempt with a short fixation and careful treatment in the 



