2l6 



THE BEGINNINGS OF IIFE. 



differed very much in shape and size — some were not 

 more than tchjct"? whilst others were as much as jio" 







"""V"-' 



Fig. 57. 

 Segmentation of Embryonal Areas into Monads. ( X 1670.) 



a. First stage of differentiation. 



b. Second stage — area almost homogeneous and refractive. 



c. First traces of segmentation. 



d. Segmentation more complete — units highly refractive. 



e. Units less refractive — forming tailless corpuscles. 



/. Fully-developed Monads derived from such corpuscles. 



in diameter. Their shape was wholly irregular. Care- 

 ful examination with a yV and a .^y immersion ob- 



