HISTOLOGY OF EPITHELIAL AND CONNECTIVE TISSUES. 31 



2. The Metaphase. The two centrosomes are at opposite ends of the long 

 avis of the nucleus, each surrounded by an attraction sphere, now called 

 the polar radiation. The chromosomes become yet shorter and thicker, 

 and move toward the equator of the nucleus, where they lie with their 

 closed ends toward the axis, presenting the appearance, when seen from 

 the poles, of a star the so-called mother star, or monaster. While 

 moving toward the equator of the nucleus, and often earlier, each chromo- 

 some undergoes longitudinal cleavage, the sister loops remaining together 

 for a time. Upon the completion of the monaster, one loop of each pair 

 passes to each pole of the nucleus, guided, and perhaps drawn by the 

 threads of the nuclear spindle. The separation of the sister segments 

 begins at their apices, and as the open ends are drawn apart they remain 

 connected by delicate achromatin filaments drawn out from the chromo- 

 somes. This separation of the daughter chromosomes, and their move- 

 ment toward the daughter centrosomes, is called metakinesis. As they 

 approach their destination, we have the appearance of two stars in the 

 nucleus the daughter stars, or diasters. 



3. 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 con- 

 stricted 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 related to some specific function. When 

 arranged in layers or strata, the cells are cemented together by an inter- 

 cellular substance mucin. 



The epithelial tissue forms a continuous covering for the surfaces of the 



