THE EARLY DEVELOPMENT OF AMIA. 4.43 
Fic. 18.—Karly embryo; tail region of embryo of Fig. 17. 
Fic. 19.—Early embryo showing head region; its length surrounds about 
220° of the ege’s circumference. Six somites present. 100 hours. 
Fie. 20.—Early embryo; tail region of embryo of fig. 19. 
PLATE 31. 
Vertical sections of cleavage stages and of blastula. x about 55. 
Fre. 21.—Second cleavage; sectioned parallel to a cleavage plane through 
the resting nuclei. 
Fie. 22.—Third cleavage; sectioned near and parallel to the plane of the 
second cleavage. 
Fie. 23.—Third cleavage; sectioned in a plane passing through the points 
*—* of Pl. 1, fig. 4. 
Fig, 24.—Fourth cleavage; sectioned in a plane (slightly oblique) near and 
parallel to the first (or second) cleavage. 
Fic. 25.—Fifth cleavage. 
Fie. 26.—Sixth cleavage. 
Fic. 27.—Seventh cleavage. 
Fic. 28.—Kighth cleavage. 
Fie. 29.—Harly blastula. Eleven hours after first cleavage. 
Fig. 30.—Blastula. Thirty-three hours after first cleavage. 
a. Central blastomere. e. Entoblast. e’. Epidermic stratum of ectoblast. 
gyb. Germ yolk blastomere. m. Merocyte. m’. Blastomere arising from 
merocyte-bearing germ-yolk. x. Nucleus. sc. Segmentation cavity. y. Yolk. 
yg. Germ-yolk. 
PLATE 32. 
Vertical sections of gastrulation stages and of early embryos. 
Fie. 31.—Early gastrula (47 hours), nearly sagittal section. x 35. 
Fie. 32.—Gastrula (50 hours), nearly sagittal section. 
Fic. 33.—Gastrula (55 hours), nearly sagittal section. 
Fic. 34.—Late gastrula (or early embryo) (75 hours), nearly sagittal 
section. 
Fig. 35.—Early embryo (78 hours); section slightly oblique to embryo’s 
axis, passing through the region of the closed blastopore. x about 70. 
Fic. 36.—Early embryo (78 hours) ; transverse section passing through 
the region of the hind brain. Xx about 70. 
