87 



is filled by a mass of cells whose boundaries and nuclei 

 are often quite difficult to make out (fig. 53). The reason 

 is that the cells are filled with refringent granules (fig. 53, 

 C. gr.), possessing great affinity for eosin stains. These 

 granules when stained mask the nuclei. Under low 

 powers of the microscope the substance of the lamellae 

 looks therefore like a granular or even fibrous mass of 

 connective tissue. In places, cells occur possessing none 

 of these peculiar contents, and as a result cell boundaries 

 and nuclei are easily determined, and the whole looks like 

 an island of cells (fig. 53, C. r.) in the midst of the dense 

 staining mass. In many cases it actually appears as if 

 the granules were first developed in the nuclei. 



Finally, one finds blood lacunae occurring amidst 

 the mass of cells as in the filaments. 



Nephridial Gland. 



The structure of the nephridial gland is exceedingly 

 interesting. It is composed of a somewhat compact 

 lymphoid tissue, a fibrous groundwork with numerous 

 lymph cells. Everywhere blood lacunae are to be seen. 

 The most striking feature, however, is the presence of 

 long canals, evaginations of the wall of the renal organ, 

 which extend into the nephridial gland and end blindly. 

 Sometimes the canals branch slightly before terminating. 

 The canals are about r ^ mm. in diameter and are lined by 

 ciliated cells. There is no trace of any opening between 

 the nephridial gland and the lumen of the renal organ. 

 The function of the nephridial gland does not appear to 

 have been satisfactorily ascertained. This kind of state- 

 ment recurs too frequently in descriptions of invertebrate 

 structures. The injections made in the course of this 

 work give only the negative result that the gland is not 

 excretory like the renal organ. The experiments were, 



