Chap. I.] 



CELLS. 



this process of division. Not long after, each of the 

 two daughter elements undergoes cleavage or division 



Fig. 3s. Verticil Section through the Ovum of Buf> Cinereus, in the 

 early stage of the Embryo Development. 



a, Tegmental laver of epiblast ; b, dorsal groove ; c, rudi nent of central nervous 

 system; d, notochnrd ; e, deep layer of epiblast ; /, mesnblast ; f, hypoWartj 

 *, cavity of alimentary canal Rusconi's cavity ; H, central yolk ; *, remainder 

 of von baer's or segmentation cavity. (Handbook.) 



into two new elements, the nucleus having previously 

 divided into two, so that each of the new offsprings 

 possesses its own nucleus. This process of division is 

 continued in the same manner for many generations 



