ON THE DEVELOPMENT OF NEBALIA. 431 



Fig. 1 7. — Transverse section through the anterior part of the optic seg- 

 ment in Stage C, behind Fig. 16. op.in. Optic invagination. 



Fig. 18. — Transverse section through the optic segment in the region of 

 the ganglion in Stage C. 



Fig. 19. — Transverse section through the posterior end of the optic gan- 

 glion in Stage C, at its junction with the ganglion of the first antenna. 

 Fig. 20. — Transverse section through the first antennae in Stage C. 



PLATE 18. 

 Fig. 21. — Transverse section through the second antenna in Stage C. 



Fig. 22.— Transverse section through the mandibular segment in Stage C, 

 showing ganglion. 



Fig. 23. — Longitudinal section through Stage C, showing the first four 

 appendages and the first three ganglia. 



Fig. 24. — Transverse section through Stage C, just in front of the mouthy 

 showing the labrum. 



Fig. 25. — Transverse section through the mouth of Stage C. 



Fig. 26. — Longitudinal (nearly median) section through Stage C. 



Fig. 27. — Section through vitellophag in Stage C. 



Fig. 28. — Transverse section through the anterior region of the optic 

 thickenings in Stage D, in front of the optic ganglia, d. Depression. 



Fig. 29. — Transverse section through the optic thickenings in Stage Dj 

 going through the most anterior region of the optic ganglia. 



Fig. 30. — Transverse section through the optic thickenings in Stage D, 

 behind Fig. 29, showing the optic invagination and the ganglion. 



Fig. 31. — Transverse section through the posterior region of the optic 

 thickenings in Stage D. cm. Central mass. 



Figs. 32 — 34. — Transverse sections through the hindmost part of the optic 

 segment in Stage D. 



Fig. 35. — Transverse section through the most anterior part of segment II 

 in Stage D, showing the ganglia of the autennules and the central mass of 

 nerve tissue lying between them. 



PLATE 19. 



Fig. 36. — Transverse section through the middle region of segment II in 

 Stage D. 



Fig. 37. — Transverse section through the hindmost region of segment II 

 n Stage D. 



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