COINTEISTS. 



Introduction p. 1. 



Methods » 3, 



The ovum, its maturation and impregnation » 7. 



The segmentation of the ovum » H. 



The Blastula stage » 19. 



The Gastrula stage » 24. 



The formation of the Mesench3'me $ 26. 



The formation of calcareous deposits » 34. 



The development of the Pluteus » 39. 



The development of the young Sea-urchin . j, 47. 



