Parker. — Lobster Eye. 



PLATE IV. 



All figures on this plate, except Fig. 59, illustrate the development of the 



lobster's eye. 

 Fig. 46. A transverse section of an optic lobe at stage E (see page 2). The plane 

 of section and the method of coloring the figure are the same as in 

 Fig. 45. x 145. 



" 47. An enlarged drawing of that portion of the retina which is in brackets in 

 Fig 46. Stage E. x 460. 



" 48. A view of the external surface of the retina. The distal ends of four 

 ommatidia are seen. Stage E. x 460. 



" 49. A transverse section of four ommatidia in the region of the hypodermal 

 nuclei. (Compare Fig. 47.) Stage E. x 460. 



" 50. A transverse section of four ommatidia in the plane which the nuclei of 

 the cone-cells occupy. Stage E. X 460. 



" 51. Longitudinal section of a single ommatidium. Stage F. X 460. 



" 52. Four corneal facets seen from the external surface. Stage F. X 460. 



" 53 to 58 represent transverse sections of four ommatidia at Stage F. The 

 numbers on the left side of Fig. 51 indicate the heights at which these 

 sections were taken, and correspond to the numbers of the following 

 figures. In Figs. 53 to 58 the magnification is 460. 



" 53. A transverse section in the region of the corneal hypodermis. 



" 54. A transverse section through the region in which the nuclei of the cone- 

 cells occur. 



" 55. A transverse section in the same plane as the nuclei of the distal 

 retinulae. 



" 56. A transverse section of the proximal ends of two cones. 



" 57. A transverse section through the rhabdomes and proximal retinulae. 



" 58. A transverse section of a rhabdome from Fig. 57. Fig. 58 was drawn 

 with a higher magnification than Fig. 57 in order to show the relation 

 of the proximal retinulae to the segments of the rhabdome. X 640. 



" 59. A corneal facet from near the periphery of the retina in an adult lobster. 

 The hexagonal outline is noteworthy. This specimen was cleaned in 

 boiling potassic hydrate and examined in water, x 280. 



