58 THE TISSUES OF PLANTS 



and so on ; so that in place of one cell we have 2, then 4, 8, 

 16, 32, 64, until the whole yolk assumes a mulberry-like 

 appearance. The cells now begin to manifest their individu- 

 ality, and gradually develope into the form of the future 

 worm. 



Fig. 14. 



Successives stages of segmentation, in the vitellus of the ovum of Ascaris acu- 

 minata. A, recently impregnated ovum, with yolk-bag slightly separated 

 from the enveloping membrane ; B, first fission into two halves ; C, second fission 

 forming four segments ; D, E, and P, formation of mulberry mass by further seg- 

 mentation ; G, the mass of cells showing the form of the future worm ; H, the 

 worm formed by the conversion of the yolk-cells, now nearly* mature. CAR- 

 PENTER. 



In most of the animal tissues the multiplication of 

 cells by division takes place during the embryonic state of 

 development, but in some cartilages it appears to take place 

 throughout the whole period of their life. Most of the 

 articular cartilages which cover the ends of the bones retain 

 their primitive cellular organization, which may be seen at 

 any time. Fig. 15 shows the successive steps in the mul- 

 tiplication of cartilage cells. In this process, as in all the 

 other acts of cell-life in animals, the nucleus seems gene- 

 rally to take a more conspicuous part than it does in plants. 



