Parker. — Lobster Eye. 



EXPLANATION OF FIGURES. 



All the figures were drawn with the aid of an Abbe* camera. Unless otherwise 

 stated, the figures are from specimens stained with Grenadier's alcoholic borax- 

 carmine and mounted in benzol-balsam. Where sections have been depigmented 

 the reagent employed was an aqueous solution of potassic hydrate i% (see Par- 

 ker, '87, p. 175). Figs. 1 to 36 refer to the histology of the adult lobster's eye. 

 Figs. 37 to 59 inclusive deal with the development of the eye. 



PLATE I. 



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



Fig. 1. A longitudinal section of an ommatidium. This is a composite figure, its 

 parts having been drawn to one scale from various sections, and after- 

 wards combined. The distal retinula on the right side of the cone 

 contains its natural pigment; that on the left side has been depig- 

 mented. The letter x indicates the position of the band which limits 

 the corneal facet. The numbers to the right of the figure correspond 

 to the numbers of the following figures of transverse sections, and 

 mark the level at which the latter were taken. X 105. 



The remaining figures on this plate (Nos. 2-25) are transverse sections 

 either of ommatidia or bundles of nerve-fibres. In each case the sections were 

 studied and drawn from their distal faces. Figs. 2 to 20 are magnified 375 

 diameters ; Figs. 21 to 25, 575 diameters. 



" 2. A corneal facet. This specimen was cleaned in a boiling solution of 

 potassic hydrate and studied in water. 



" 3. Four pairs of cells from the corneal hypodermis. Around the lower right- 

 hand pair of cells the outlines of the six surrounding distal retinulae are 

 indicated in part by dotted lines. 



" 4. Four groups of cone-cells. The ommatidia to which the cone-cells be- 

 long are indicated by the letters a, b, c, and d. These letters are used 

 to indicate corresponding ommatidia in deeper sections. 



" 5 to 20 represent transverse sections through ommatidia in the various regions 

 indicated as follows : — 



" 5. The middle region of four cones. Completely depigmented. 



" 6. The proximal ends of four cones. The re-entrant angle on the surface is 

 indicated at x. Completely depigmented. 



" 7. Slightly below the proximal ends of the cones. 



" 8. Beyond the distal ends of the proximal retinulae. 



" 9. The distal ends of the proximal retinulae. 



" 10. The thick distal portion of the proximal retinulae. 



" 11. The proximal retinulae immediately above the distal termination of the 

 rhabdome. 



" 12. At the distal ends of the rhabdomes. Completely depigmented. 



