FREE CELLS AND EPITHELIUM. 5 



is, when it has reached maturity — its protoplasm commences to 

 separate into two equal halves. This division is preceded by a 

 corresponding separation of the nucleus, and then the whole cell 

 splits into two cells. During this process of cell-division certain 

 definite changes take place in the nucleus. This body at first 

 is spindle-shaped ; its contents are drawn out into longitudinal 

 striae, when the centre of these strise becomes thickened and 

 forms an equatorial zone or " nuclear plate." This " plate " 

 divides, and each half travels to the poles of the spindle, which 

 assumes a dumb-bell shape, then elongates, and the two nuclear 

 masses, the remains of the equatorial plate, become surrounded 

 by a clear fluid mass. These form the two nuclei at the 

 poles of the spindle. As soon as this has taken place the 

 whole protoplasm constricts in the middle, and the cell 

 divides into two. 



There are two other ways in which cells reproduce — namely, 

 by "budding" and by "endogenous cell- formation." "Bud- 

 ding " is when one of the produced cells is smaller than the 

 parent cell. In " endogenous cell-formation " we get the proto- 

 plasm and nucleus of the parent cell, splitting up internally 

 into a number of small bodies, known as " spores." These are 

 seen only in the lowest forms Of life. 



The separation of groups of various cells leads to the forma- 

 tion of the different tissues. Of tissues we make out two 

 chief kinds — namely, vegetative tissues and animal-life tissues. 

 The former carry out the nourishment and maintenance of 

 the body ; the latter are those tissues which are characteristic 

 of animals, and whose functions are for movement and 

 sensation. 



Of vegetative cell-tissues there are two divisions — (1) epi- 

 thelium and free cells, and (2) connective tissue substances. 

 The tissues of animal-life are (3) muscular tissue and (4) 

 nervous tissue. 



1. Free Cells and Epithelium. 



(a) Free, w wandmng cells are those that are found floating 



