BIGELOW. Development of Lepas. 



PLATE 1. 



Figures in this plate are all from living eggs, and represent stages between 

 oviposition and the close of the first cleavage. The small circles represent the 

 oil spherules which are embedded in the yolk. 



Fig. 1. Egg about thirty minutes after oviposition. Vitelline membrane and 

 second polar cell have appeared. Yolk uniformly distributed in the 

 egg. 



Figs. 2-5. Egg elongating. Protoplasm concentrating in upper half of the egg. 

 Yolk becomes aggregated at the vegetative pole. Development of yolk- 

 lobe. 



Fig. 6. Yolk-lobe has disappeared. Yolk radially symmetrical with reference to 

 chief axis of egg. Vitelline membrane has assumed its definitive form. 



Fig. 7. Yolk moves to eccentric position with reference to the chief axis. 



Figs. 8-15. First cleavage. Time thirty minutes. Drawings made at intervals of 

 about four minutes. Rotation of the dividing egg within the vitelline 

 membrane. 



Fig. 16. One hour after close of first cleavage (Fig. 15). Yolk has returned some- 

 what toward the vegetative pole. 



