PLATES 



I. Tests of Arbacia punctulata 

 11. Maturation of the egg; polar body formation 



III. Normal development of the living egg from one cell 

 to gastrula 



IV. Normal development, continued; gastrula to pluteus 

 V. Stained sections of developing eggs 



VI. Metamorphosis 



VII. Breaking of unfertilized egg by centrifugal force 



VIII. Development of centrifuged eggs, elongate and spherical 



IX. Development of white half-egg 



X. Development of red half-egg (fertilized) 



XI. Development of red half-egg (parthenogenetic) 



XII. Development of clear quarters and eggs centrifuged 

 after fertilization 



XIII. Stratification and size of half-eggs in relation to cen- 

 trifugal force 



XIV. Stratification and size of half-eggs in hypo- and hyper- 

 tonic sea water 



XV. Stratification and breaking of eggs, centrifuged in 

 single salt solutions 

 XVI. Miscellaneous photographs 



