66 



CELL-DIVISION AND GROWTH 



II. 2 



nucleus and cytoplasm is reached (Boveri) (see below, p. 268). 

 Minot suggests that ' senescence ' and differentiation alike depend 

 on an increase in the protoplasm. 



10% 



5%' 



120 % 



no%- 



100 %- 

 90%- 

 80% 

 70 % 

 60% 

 50%- 

 40 % 

 30 % 

 20% 

 10% 



Aboral Arm -Length. 

 Oral Arm-Length. 

 Body-Length. 



Pluteus of Stronyylocentroins livtdus. 



iiojll 12 'l3 14 15 'lG Days. 



Shell-length of Limnaea stagnalis. 



I T 



i r 



I I [ 



i i i i 



Days. 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 



FIG. 38. Curves showing the change with age of the rate of growth 

 in the larva of the sea-urchin Strongylocentroiiis (from Vernon's data), 

 and the pond-snail Limnaea (from Semper's figures). The abscissae are 

 days, the ordinates percentage increments. 



