PLATE 2 



EXPLANATION OF FIGURES 



All figures are from Strongylocentrotus except 11. All drawings were made 

 with a camera lucida except 10 which is from a free hand sketch. Magnifica- 

 tion varies as noted below. 



10 Protoplasmic movement in later division cycle. X 1100. 



11 Protoplasmic movement in Arbacia egg showing migration of pigment. 

 X 1200. 



12 and 14 Monaster eggs beginning second division cycle. X 1200. 



13 and 15 Consecutive sections through a monaster egg during the proto- 

 plasmic movement. X 1000. 



490 



