110 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate IV. — Asellus communis. 



Fig. 19. Transver.se section of the head tliroughthe proeerebral lobes and through the eyes and optic nerves and com- 

 missures X i A. 



Fig. 20. A section back of the procerebruui passing through the optic ganglion, optic nerve and eye. 



Fig. 21. Same section as in Fig. 20, enlarged X i A, re, retinal cells ; op, n, optic nerve; h, i, k, masses of ganglion cells. 



Fig. 22. Horizontal section through the main commissures and the first and second m.axillary ganglia, and niaxillipedal 

 ganglia, and showing the origin of the mandibular nerves. X i A. 



Fig. 2o. The same section as in Fig. 22, enlarged, x '- A. 



Plate V.— C^cidot^a stygius. 



Fig. 25. Transverse section through the procerebruui and commi.ssures. x ■; A. 



Fig. 26. .Section a little posterior to that of Fig. 25. X + A. 



Fig. 27. Enlarged sketch of section still farther back, x i A. 



Fig. 28. Enlarged sketch of section still farther back. X i A. 



Fig. 29. Section behind procerebruui and showing the rudimentary eye, but entire ab.sence of the optic ganglion and 



optic nerve. 

 Fig. 30. Section through the eye. x ^ A. 



Fig. :il. Section through the eye of another individual. X i A. c, lens. X i c. 

 Fig. 32. Section through a ventral ganglion. 

 Fig. 33. Section through a ventral ganglion. 

 Fig. 34. Section through a ventr.al ganglion under the stomach. 

 Fig. 35. Section through a ventral ganglion under the stomach. 



Note. — All the figures drawn by the author with the camera lucida. 



