FORMATION OF GERM-LAYERS IN ORANGON VULGARIS. 363 
Fie. 13.—Portion of a section through the centre of the egg at the close of 
segmentation. 
Fic. 14.—Section passing through the blastopore at the stage shown in 
Fig. 5. 
Fie. 15.—Median longitudinal section through an embryo of the age of 
Fig. 6. 
Fic. 16.—Lateral section from the same series. 
Fies. 17—21.—Transverse sections through an embryo slightly older than 
Fig. 6. 
Fie. 22.—Posterior portion of an obliquely longitudinal section through 
an embryo of the age of Fig. 6, showing cavity in the endoderm. 
Fies. 23—27.—Successive transverse sections through an embryo of the 
age of Fig. 7. 
Fic. 28.—Transverse section through the optic ganglion at the age of 
Fig. 8. 
Fic. 29.—Transverse section through the thoracico-abdomen at the age 
of Fig. 8. 
Fic. 30.—Horizontal section through the abdominal papilla, at stage 
between Fig. 8 and Fig. 9. 
Fies. 31—33.—Successive horizontal sections through the abdominal 
papilla at the age of Fig.9. The sections are parallel to the line x y in Fig. 
34, and perpendicular to the plane of the paper. 
Fig. 34.—Slightly lateral longitudinal section through Fig. 9. 
