ON THE EYES OF SOME INVERTEBRATA. 681 



such eyes have been inherited from an ancestor common to 

 these different classes and orders. 



EXPLANATION OF PLATE XLV. 



Illustrating Dr. Justus Carriere's Memoir " On the Eyes of 

 Some Invertebrata," 



Fig. 1. — Vertical section of the eye of Musca voir.itoria. Stained 

 with Haematoxylin. a. Au ommatidium (eye-unit), more highly magnified. 

 c. Cornea. /. Fold of the chitinous membrane, y. Ledge of chitin. 1. Pseu- 

 doconus. 2. Pigment-cells (i). 3. Pigment-cells (ii). 4. Crystal-cells. 

 5. Rhabdomere. 6. Retinula. 7. Pigment-cells on the base of the retinula. 

 8. Basal membrane, with its matrix-cells. 9. Layer of little cells. 10. Layer 

 of palisade cells of the peripheral ganglion-opticum. 11. Membrane. 13. 

 Chiasma of nerve-fibres. 13. Central ganglion-opticum. 14. Intermediate 

 ganglion. 



Fig. 2. — A vertical section through the midst of the eye of Leptodora 

 hyalina. b. An ommatidium of it, more highly magnified, a—d. Transverse 

 sections through the crystal cone. a. Near the base. b. In the first third. 

 c. In the second third, d. Close before the retinula. g. Ganglion-opticum. 



Fig. 3.— Vertical section of the eye of Pectunculus glycimeris. 



1. Epithelial cells. 2. Optic cell (nerve-end cell). 3. Connective tissue and 

 nerve-fibres. 4. Transverse section of three nerve-end cells, in two of 

 them the nucleus. 



Yvn. 4.— Vertical section of the eye of Area Noae. 1. Epithelial cells. 



2. Nerve-end cell, tangential section. 3. Nerve-end cell, median section. 4. 

 Transverse section of a nerve-end cell. 5. Connective tissue and nerve-fibres. 



