HISTOLOGY. 



FIG. 4. VACUOLES IN YOUNG 

 FAT CELLS. 



Capsule. 

 FIG. 



Canaliculi. 



ANALS (TROPHOSPONG- 

 IUM) IN A NERVE CELL. 



3. Vacuoles. Well defined, round spaces, 

 apparently empty, may occur in the protoplasm 

 due to the formation of droplets of fat or of watery 

 fluids. They vary greatly in size, and one or sev- 

 eral of these vacuoles may be found in a single cell. 



4. Canals, of two sorts, (a) Secretory canals 

 which occur in protoplasm of gland cells and 

 empty into the gland cavity or lumen; (b) fine 

 tubes which communicate with lymphatic spaces 

 outside of the cell. They are found in all cells of 

 higher physiological importance, but are lacking 

 in most of the supporting tissues and in stratified 

 epithelium. They presumably share in nourish- 

 ing the cell and have been called the "tropho- 

 spongium." This name, implying a network, 

 is due to the opinion, not established, however, 

 that the little canals are occupied by cell proc- 

 esses extending into the protoplasm from adjoin- 

 ing "capsule cells." Other investigators consider 

 that the trophospongium canals are wholly within 

 the cell and constitute a form of vacuole. 



5. Closed networks, which do not open at 

 the periphery of the cell. This "reticular appa- 

 ratus" has been found in nerve, cartilage and 

 many gland cells. Its significance is unknown. 



6. Inclusions. These are foreign bodies 

 which have been ingested by the cell and are 

 found in the protoplasm. Inert crystalloid sub- 

 stances formed within the cell are also called 

 inclusions. The name " paranucleus " has been 

 applied to various structures, such as a dead cell 

 ingested by a living one, a transformation of the 

 centrosome, or a mass of secretion. Some of the 

 paranuclei are still obscure. 



NUCLEUS. 



The nucleus (Latin, nucleus, "the kernel of 

 a nut"; Greek, xdpvov, "a nut") is a well defined, 

 refractive body of vesicular form situated within 



the cell. It consists of a membrane enclosing a mass of ground substance, 

 or nuclear sap, in which there is a fibrillar network associated with some 



Reticular apparatus. 



FIG. 6. RETICULAR NETWORK 

 IN A NERVE CELL. (After 

 Golgi.) 



FIG. 7. CRYSTALLOID INCLU- 

 SIONS. INTERSTITIAL CELLS 

 OF THE TESTIS. 



