Chap. I.] 



CELLS. 



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

 two daughter elements undergoes cleavage or division 



Fig. SB. Vertical Section through the Ovum of Bufo Cinereus, in the 



early tage of the Embryo Development, 

 a, Tegmental layer of epihlast ; 6, dorsal groove; c, rudiment of central nervous 



pyptem ; d, notochord ; e, deep layer of epiblast ;/, niesoblast ; g, hypobla?t ; 



h, cavity of alimentary canal Rusconi's cavity ; H, central yolk ; k, 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 offspring 

 possesses its own nucleus. This process of division is 

 continued in the same manner for many generations 



