66 KINGSLEY. [Vol. I. 



EXPLANATION OF PLATE. 

 Reference Letters, 

 b, bacilli. 



c, crystalline cone. 



e, ectoderm or epidermis. 



g-, gangliogen. 



gt, rows of ganglionic nuclei. 



k, entoderm or hypoblast. 



/, corneal lens. 



tn, mesoblast. 



o, ommatidium. 



oc, optic cavity. 



og, optic ganglion. 



oi, optic invagination. 

 ol, optic lobes. 

 fii-f\, pigment-cells. 

 ■pd, pedicle, 

 r, retinogen. 

 rp, retinophora. 

 rt, rows of retinal nuclei. 

 sg, supra-oesophageal ganglion. 

 X, undifferentiated ventral surface of 

 the body. 



The figures were all drawn with the Hartnack microscope and Oberhauser's 

 camera, unless stated to be diagrammatic. The amplification is stated in 

 most instances. 



Figure i. Surface view of a stained ^^^ at the time of the appearance 

 of the optic lobes. (X 25S.) Every nucleus was drawn Avith a camera, except 

 those on the extreme margin. 



Fig. 2. Transverse section through an optic lobe of Fig. i, the left side 

 being toward the median line. (X 550.) 



Fig. 3. Optic lobe at about the time of closure of the optic invagination. 

 (X 840.) 



Fig. 4. Optic cavity and surrounding portions at a stage when one ap- 

 pendage is outlined. (X 575-) 



Fig. 5. Same when two appendages are outlined. (X 550.) 



Fig. 6. Eye at time when seven appendages are outlined. The upper is 

 the more dorsal portion. (X 550.) 



Fig. 7. Section through half the head at the time of first deposition of 

 pigment, showing the relationships of optic and cerebral ganglia and eye. 



Fig. 8. Retinal and epidermal elements of same eye still more enlarged. 



Fig. 9. Surface view of pigment at time of first appearance in the same 

 eye. Drawn from living embryo. 



Fig. id. Three retinal elements (one retinophora and two pigment cells) 

 teased from a section of an eye in the stage of Fig. 11. Free-hand drawing. 



Fig. II. Portions of three ommatidia of an embryo nearly ready to 

 hatch. (X 700.) 



Fig. 12. Half of cephalic region of embryo, same age as Fig. 6, showing 

 the mesoderm, etc. (X 260.) 



Fig. 13. Diagram of a single ommatidium of Fig. 11, to show the relations 

 of the pigment-cells, retinophorae, crystalline cone, and pedicle. The length 

 of the crystalline cone and the distances between the outer pigment-cells are 

 exaggerated for sake of clearness. 



