PLATE II. 



Fig. 13. Posterior view of embryo containing 74-80 cells. 



Fig. 14, Posterior view of a later stage. Bilateral division of 4^. 

 Rudimentary cell budded off in the d intermediate girdle region. 



Fig. 15. Ventral view of 64-cell stage. 



Fig. 16. Ventral lateral view of 86-cell stage. Fifth quartet 

 forming. 



Fig. 17. Ventro -posterior view of 86-cell stage. Further divi- 

 sions in the X group. 



Fig. 18. Ventral view of a later stage. Fifth quartet formed. 

 Bilateral cleavage of 4^. 



Fig. 19. Postero-ventral view of the same stage. 



Fig. 20. Postero-ventral view of a slightly later stage. Rudi- 

 mentary cell budded off in the X group, ^d has divided. 



Fig. 21. Beginning of gastrulation. 3<'/2 2.2.1 » '^^-'^^^ ^ctomesoblast left 

 and 31^2.1.2.1, emr, ectomesoblast right have invaginated. 3^2.2.25 einm, 

 ectomesoblast median is sinking in. 



Fig. 22. Fourth quartet has divided. ^;;/;;/, ectomesoblast median, 

 about to divide. 1^ -I2. cells beginning to migrate through the dorsal 

 gap. oes.r^ oesophagoblast right. 



Fig. 23. Entoblast plate has almost entirely invaginated. 2/^2.21.2. 

 {oes m), oesophagoblast median, has increased in size. Nine-hour 

 embryo. 



Fig. 24. Gastrulation completed. Small entoblasts budded off 

 from the coelomesoblast {^M — M) cells. Ectomesoblast cells have 

 all divided. Migration of /, — 4 cells, oes.l, oesophagoblast left. 

 Ten-hour embryo. 



(246) 



