22 



INTRODUCTION PEOTOPL ASM CELL 



medulla of the adrenal, and in decidual cells. In ciliated epithelia this 



mode of division is perhaps associated with a partition of the centro- 



some in the formation of cilia. This will be further discussed under 



a Ciliated Epithelia. 



This view is sup- 

 ported by the fact 

 that the flagella of 

 spermatozoa arise 

 from the centro- 

 some, and the ob- 

 servation that in 

 certain cells the 

 centrosome of mi- 

 totic spindles de- 

 velops cilia (Fig. 

 27). 



(b) MITOSIS. 

 This is the prevail- 

 ing type of cell di- 

 FIG. 29. CELLS FROM EPIDERMIS OF THE SALAMANDER. vision. For con- 

 Three cells are in process of division by mitosis, a, venience of descrip- 

 prophase; 6, anaphase. The second cell above b, whose {ion ^] ie process 

 cell body is in process of fission, presents a stage of the 1-1 e 



telophase. (After Wilson.) which mus 



course be thought 



of as continuous, may be divided into (1) prophase; (2) metaphase; (3) 

 anaphase; and (4) telophase. An alternative and preferable terminology 

 employs the words anaphase (prophase), mesophase (metaphase) and 

 kataphase (anaphase and telophase). These phases involve coincident 

 changes in the nucleus and the archoplasm (attraction sphere, Fig, 28, A 

 to J). Mitotic figures can be seen in all rapidly growing tissues. The 

 process is an essentially similar one throughout the plant and animal 

 kingdoms; variations relate only to details associated chiefly with the 

 archoplasm. The most favorable locations for study of mitosis are the 

 growing tips of roots of certain plants, e.g., onion, hyacinth, dogtooth 

 violet, amphibian tissue (particularly skin and blood-cells), and the 

 testes of grasshoppers. Mitosis in germ cells involves certain specialized 

 features, and calls for additional theoretical consideration; hence the 

 description of these maturation mitoses will be reserved for the chapter 

 dealing with the ovaries and testes, where a complete account will follow. 

 Among the simplest types of mitosis, and those best adapted for labora- 



