MUSEUM OF COMPARATIVE ZOOLOGY. 273 



vL c. Vitelline cells forming a "protoplasmic network" through the yolk contents. 



In many of the figures only a few of these cells are drawn. They ai'e 



found throughout the whole contents of the egg. 

 y. Unknown body, possibly remnant of membrane which encloses the egg. 



All the figures, with the exception of PI. IV. figs. 3-7, were drawn by the author 

 with an Oberhauser camera, objective B. B., eye-piece 2, Zeiss. Size reduced one half 

 in photography. All figures except PI. II. fig. 2 were drawn from living eggs and 

 larvae. The last mentioned was treated with dilute acetic acid before drawing. 



PLATE I. 



Fig. 1. Immature female gonophore with egg in the interior. Nucleus and nucle- 

 olus shown through its walls. Attached to parent. 



" 2. Egg in a small inmiature gonophore, with sinuses between ovum and bell 

 walls of gonophore. 



" 3. Female gonophore found free in water. Enclosed ovum .5 mm. in diameter. 



" 4. The ovum in the act of escape from the gonophore. 



" 5. Ovum removed fi'om a gonopliore (artificially). 



" 6. Ovum just escaped from gonophore (naturally), .45 mm. in diameter. 



" 7. Egg showing the formation of a primitive furrow at one pole. 



" 8. The same, ten minutes older than last. 



" 9. The same, fifteen minutes older. 



" 10. The same, twfmty minutes older. 



" 11. The same, twenty-five minutes older. 



" 12. The same in two-cell stage, thirty minutes older than Fig. 7. Diameter 

 .3.5 mm. The egg traced from Figs. 7-12 is .1 mm. smaller than that 

 from Fig. 13 on. 



" 13. Two-cell stage with beginning of a secondary furrow (sc), .60 mm. in long 

 diameter, . 43 mm. in least diameter. 



" 14. Two-cell stage, ten minutes older than Fig. 13. .60 mm. in diameter. 



"15. The same, fifteen minutes older. 



" 16. The same, eighteen minutes older. 



" 17. The same, twenty minutes older. 



" 18. The same, twenty-five minutes older, showing the formation of the sec- 

 ondary furrow, extending in a horizontal direction over the surface of 

 the ovum. It also shows tlie deviation of the primary cleavage plane 

 (1 cL pi.) fiom a straight line when seen in profile. 



" 19. Formation of a 4-cell stage by the closing in of the secondaiy furrow (sc). 

 The furrow is still open at each end. Thirty minutes older than Fig. 

 13, .50 mm. in diameter. 



" 20. Four-cell stage, thirty-five minutes after Fig. 13. 



" 21. The same, forty-five minutes after. 



" 22. The same, fifty-five minutes after. 



" 23. The same, one hour and ten minutes after. 



VOL. XI.— NO. 11. 18 



