HISTOLOGY OF EPITHELIAL AND CONNECTIVE TISSUES. 35 



apart they remain connected by delicate achromatin filaments 

 drawn out from the chromosomes. This separation of the daughter 

 chromosomes, and their movement toward the daughter centro- 

 somes, is called metakinesis. As they approach their destination, 

 we have the appearance of two stars in the nucleus the daughter 

 stars, or diasters. 



. Anaphase. The daughter stars undergo, in reverse order, much 

 the same changes that the mother star passed through. The 

 chromosomes become much convoluted, and perhaps united to one 

 another, the lateral twigs appear, and the chromatin resumes the 

 appearance of the resting nucleus. The nuclear spindle, with 

 most of the polar radiation, disappears, and the nucleoli and the 

 nuclear membrane reappear, thus forming two complete daughter 

 nuclei. Meanwhile the protoplasm becomes constricted midway 

 between the young nuclei. This constriction gradually deepens 

 until the original cell is divided, with the formation of two com- 

 plete cells. 



HISTOLOGY OF THE EPITHELIAL AND 

 CONNECTIVE TISSUES. 



i. EPITHELIAL TISSUE. 



The epithelial tissue consists of one or more layers of cells resting 

 on a homogeneous membrane, the other side of which is abundantly 

 supplied with blood-vessels and nerves. The form of the epithelial 

 cell varies in different situations, and may be flattened, cuboid, 

 spheroid, or columnar. The form of the cell in all instances is re- 

 lated to some specific function. When arranged in layers or strata, 

 the cells are cemented together by an intercellular substance mucin. 



The epithelial tissue forms a continuous covering for the surfaces 

 of the body. The external investment (the skin) and the internal 

 investment (the mucous membrane, which lines the entire alimentary 

 canal and its associated body cavities) are both formed, in all situa- 

 tions, by the homogeneous basement membrane, covered with one or 

 more layers of cells. All materials, therefore, whether nutritive, 

 secretory, or excretory, must pass through epithelial cells before 

 they can enter into the formation of the blood or be eliminated from 

 it. The nutrition of the epithelial tissue is maintained by the 



