Parker — Lobster E>e. 



PLATE III. 



All figures on this plate illustrate the development of the lobster's eye. 

 Fig. 40. A section through the left optic lobe and left half of the supra-oesophageal 

 ganglion. The plane of section is tangential to that part of the sur- 

 face of the egg on which the embryo rests. The position of the 

 median plane is indicated at xy. The surfaces tinted with deeper pink 

 in the figure represent areas containing nuclei in the specimen ; those 

 in lighter pink, areas in which no nuclei were present. The optic lobe 

 is divided into two parts by a band of large, faintly colored nuclei, 

 which, with the smaller surrounding nuclei, are shown in the figure. 

 To the right of the nuclei the broad tinted marginal area represents 

 the retina, r. The remainder of the optic lobe gives rise to the optic 

 ganglion. Stage C (see page 2). X 280. 



" 41. Posterior aspect of a transverse section of a right optic lobe. The plane 

 of section corresponds to that in Fig. 38 ; a: is the angle which indi- 

 cates the separation of the retinal and ganglionic constituents of the 

 intercepting membrane. Stage C. X 280. 



" 42. This figure is taken from a region which corresponds to the left-hand por- 

 tion of Fig. 41. Although from the same set of eggs the embryo from 

 which Fig. 42 was drawn was somewhat more advanced than that 

 from which Fig. 41 was taken. At x the proximal band of retinal 

 nuclei can be seen; at y the distal band is shown. Stage C. X 460. 



" 43. The superficial layer from the distal band of retinal nuclei ; seen from 

 the external surface of the retina. Stage C. x 460. 



" 44. The deep layer of the distal band of nuclei. These are seen in opti- 

 cal section somewhat within the outer face of the retina. Stage C. 

 x 460. 



" 45. A transverse section of an optic lobe from a lobster at stage D. The 

 plane of section corresponds to that of Fig. 38. As in Fig. 40, the 

 deeply tinted areas were nucleated ; the lighter areas were without 

 nuclei. X 145. 



