PLATE 3 



EXPLANATION OF FIGURES 



15 to 18 Origin of plastids by cytoplasmic constriction. 



15 Experiment 20; nineteen-hour autoplastic culture; 30 mm. embryo. For- 

 mation of large plastid. 



16 Experiment 21; nineteen-hour homoplastic culture of blood from 30 mm. 

 embryo in plasma, from 190 mm. embryo. Formation of large plastid, comparable 

 to the so-called macrocytes. 



17 Experiment 20 ; twenty-four autoplastic culture ; 30 mm. embryo. Shows the 

 partial fragmentation of the cytoplasm remaining around the nucleus (stages r, s) 

 after the completion of the cytoplasmic constriction and the origin of a small, 

 secondary plastid or microcyte from the newly formed plastid (stages l-s). 



18 Experiment 9; approximately a twenty-hour homoplastic culture of blood 

 from a 32 mm. embryo, in plasma from a 49 mm. embryo. Shows origin of a plastid 

 by a cytoplasmic constriction in which the process was of such a character as to 

 leave the nucleus unsurrounded by any evident cytoplasm. 



200 



