Plate I. 



Fig. J. Egg mass of Slphoitarla tleposiletl uu ruck. Natural size. Arrow 

 indicates the orientation of the animal during egg-de})osition. 



Fig. 2. Three eggs magnified to show their manner of connection. ]<"'resh. 

 Ax 2. 



Fig. 3. Yolk splierules with vacuoles before disintegration. Fresh. E x 2. 



Fig. 4. Egg after total disintegration of yolk spherules. 



Fig. 5. First cleavage stage, two blastomeres being connected only by a 

 narrow bridge. Fresh. 



Fig. 6. {Second cleavage stage. Its commencement, from above. Fresh. 



Fig. 7. Same stage, further advanced. 



Fig. 8. Completion of the same stage. J31astomeres are now designated as 

 A, the left anterior, B, tlie right anterior, C, the right [losterior, 

 and ]), the left posterior. 



Fig. 9. Cleavage of the first quartet of ectomere-cells. From ai)ical [)ole. 



Fig. 10. »Same stage. From posterior side. 



Fig. 11. Completion of the same stage, to show the position of cells. From 

 a[)ical pole. 



Fig. 12. Second ectomcre-quartet stage, showing its formation. A[)ical ^'i('w. 



Fig. 13. Same stage. Posterior view. 



Fig. 14. Commencement of third ectomere-quartet. Ajncal view. 



Fig. 15. Cleavage of fourth and fifth ectomere-quartets. Horizontal section. 



Fig. 16. Fifth ectomere-quartet stage with formation of entomere-cell Dj. 

 Sagittal section. 



Fig,' 17. Sixth ectomere-(|ua.rtet stage. Horizontal section. 



Fig. 18. Formation of entomere-cell Dj. Horizontal section through ve- 

 getative pole. 



Fig. 10, Same stage. Sagittal section. 



Fig. 2U. Cleavage of seventh ectomere-cpiartef. Jbjri/.ontal section through 

 vegetative pole. 



