14 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, 



Plate IV. — Asellus communis. 



Fig. 19. Transverse section of the head through the procerebral lobes and through the eyes and optic nerves and com- 

 missures X i A. 



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



Fig. 21. Same section as in Fig. 20, eularged X ^ A, re, retinal cells; o^, », optic nerve; ft, i, i:, masses of ganglion cells. 



Fig. 22. Horizontal section through the main commissures and the first and second maxillary ganglia, and maxillipedal 

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



Fig. 23. The same section as in Fig. 22, enlarged. X i X. 



Plate V.— C^crooTiEA stygius. 



Fig. 25. Transverse section through the procerebrum and commissures. X i A. 



Fig. 26. Section a little posterior to that of Fig. 25. X i 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 procerebrum and showing the rudimentary eye, but entire absence of the optic ganglion and 



optic nerve. 

 Fig. 30. Section through the eye. X i A. 



Fig. 31. Section through the eye of another individual. X ^ 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 ventral 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 Incida. 



