COMPOUND PVES OF AliTHROPODS. 331 



Fig. 35. — Cambants. The retinula completely isolated. Tiiu 

 rhiibdomere shows u coarse wavy outline, j (D X 2) Z. 



Fia. 36. — Sguilla, partly diagramatic. 



Fig. 37. — CaUincdcn, partly diagramatic. 



Fig. 38. — Serolis, partly diagramatic. 



The last three ligures are introduced here so as to show the 

 homology of the retinula cells in different groups of Arthropods. 



All the specimens figured in this plate were treated and macerated 

 in Haller's fluid. 



Plate XXXll.—Limnhis. 



Fig. 39. Young embryo of Limulus. D.O. "Dorsal organ"; 

 * shows the position where the compound eye makes its appearance. 



Fig. 40. Larval Limtihis in the so-called "trilobite stage"; imme- 

 diately after hatching. D. 0. " Dorsal organ "; E. Compound eye ; 

 Oc. Ocelli. 



Fig. 41. Young Limulus at the first stage in the acquisition of the 

 external Limuloid characters. The whole body is transparent and 

 the dendritic ramifications of the " liver " shining through the trans- 

 parent tissues of the body. The "dorsal organ" has completely 

 disappeared in this stage. E. the compound eye; and Oc. Ocelli. 



Fig. 42. Transverse section of a young larva, showing the origin 

 of the compound eye (^E), the formation of the dorsal and venti-al 

 folds of invagination {d.f and i'./), and the "dorsal organ " D. 0. 

 § (A X 2) Z. 



Fig. 43. Transverse section of the compound eye, showing the 

 formation of the optic nerve fibres by the migration of the ectodermal 

 cells. ? (D X 4) Z. 



Fig. 44. Outline of the thickening of the nerve plexus beneath 

 the ommatidial layer. I (E X 2) Z. 

 IG. 45. The same. 3 (D X 4) Z. 



Both are drawn from the gold-chloride preparations. 



Fig. 46. Ganglionic swelling found in the optic nerve fibres of the 

 median eye. j (4 X D) Z. 



Plate WXlll.—Limuhis. 



Fig. 45rt. Longitudinal section of the eye, showing the formation 

 of the optic nerve fibres {Op. n). 



Fig. 46rt. Oblique longitudinal section of the eye, showing the 

 formation of the optic nerve fibres {Op. n). 



