EXPLANATION OF PLATES 30, 31, 32. 695 



st. Stomodseum. sit. Suctorial apparatus. sn. g. Supra-<esophageal ganglion. 

 th. g. Thoracic ganglion, v. g. Ventral nerve cord, y, c. Cells derived from yolk. 

 yk. Yolk. y. n. Nuclei of yolk cells. 



I g IV g. Ganglia of ambulatory limbs, i 16. Postoral segments. 



Fig. 10. Section through an ovum, slightly younger than fig. i. Shewing 

 the primitive cumulus and the columnar character of the cells of one half of the 

 blastoderm. 



Fig. n. Section through an embryo of the same age as fig. 2. Shewing the 

 median thickening of the blastoderm. 



Fig. 12. Transverse section through the ventral plate of a somewhat older embryo. 

 Shewing the division of the ventral plate into epiblast and mesoblast. 



Fig. 13. Section through the ventral plate of an embryo of the same age as 

 fig. 3, shewing the division of the mesoblast of the ventral plate into two mesoblastic 

 bands. 



Fig. 14. Transverse section through an embryo of the same age as fig. 5, passing 

 through an abdominal segment above and a thoracic segment below. 



Fig. 15. Longitudinal section slightly to one side of the middle line through an 

 embryo of the same age. 



Fig. 1 6. Transverse section through the ventral plate in the thoracic region 

 of an embryo of the same age as fig. 7. 



Fig. 17. Transverse section through the procephalic lobes of an embryo of the 

 same age. gr. Section of hemicircular groove in procephalic lobe. 



Fig. 1 8. Transverse section through the thoracic region of an embryo of the 

 same age as fig. 8. 



Fig. 19. Section through the procephalic lobes of an embryo of the same age. 



Fig. 20 a, b, c, d, e. Five sections through an embryo of the same age as fig. 9. 

 a and b are sections through the procephalic lobes, c through the front part of the 

 thorax, d cuts transversely the posterior parts of the thorax, and longitudinally 

 and horizontally the ventral surface of the abdomen, e cuts the posterior part of the 

 abdomen longitudinally and horizontally, and shews the commencement of the 

 mesenteron. 



Fig. 21. Longitudinal and vertical section of an embryo of the same age. The 

 section passes somewhat to one side of the middle line, and shews the structure of the 

 nervous system. 



Fig. 22. Transverse section through the dorsal part of the abdomen of an embryo 

 of the same stage as fig. 9. 



