Pakker — Lobster Eye. 



PLATE II. 



Figs. 2G to 36 deal with the histology of the lobster's eye ; Figs. 37 to 39, with its 



development . 



Fig. 26. Vertical section through that portion of the eye-stalk wliere tiie transi- 

 tion from the unditlerentiated hypoderiiiis to tlie oniinateuin is accom- 

 plished. Tlie open space x is due to sliriiikage. X 31. 



" 27. A group of the four cone-cells of an oniniatidiuin and tlie attaclied cor- 

 neal hypodermis. Isolated and studied in Mailer's tluid. X 865. 



" 28. Proximal end of a group of four cone-cells where they sei)arate as fihres 

 to pass around the rhabdome. Isolated and studied ni MuUer's tluid, 

 X 365. 



" 29. Transverse section of the basement membrane. The distal face is upper- 

 most; the proximal face below. The section is taken in a plane 

 which would be represented in Fig. lil by the line z ij. x 575. 



" 30. A rhabdome and its seven surrounding proximal retinula;. At the distal 

 end the free tips of the seven retinulaj can be seen. At the i)roximal 

 end the rhabdome and the four groups of retinuhe which pass through 

 the basement membrane are visible. Isolated and studied in chromic 

 acid 3^5%. X 200. 



" 31. An individual proximal retinula. Isolated and studied in chromic acid 

 iA X 200. 



" 32. Transverse section of a rliabdome and its surrounding cells. The plane 

 of section is about half-way between the middle and distal end of the 

 rliabdome. Completely depigmented with potassic hydrate. X 400. 



" 33. Oblique section of a rhabdome from the same series of sections as Fig. 32. 

 The upper end of the figure is distal; the lower, proximal, x 4G0. 



" 34. Transverse section of a rhabdome and its surrounding retinuhr. The 

 nervous axis of each retinula is distinctly stained. Completely de- 

 pigmented ; stained with Kleinenberg's alum-luematoxylin. x 460. 



" 35. Longitudinal section of a bundle of nerve-fibres extending through the 

 basement membrane toward the optic ganglion. Depigmented ; 

 Weigert's hematoxylin, x 575. 



" 3G. Optic nerve-fibre. Isolated and studied in Midler's fluid. X 575. 



" 07. Superficial view of a left optic lobe. Enough of the right lobe is drawn 

 to indicate the position of the median plane (.r y). x is anterior; y is 

 posterior. Stage A (see page 2). x 280. 



" 38. Posterior face of a section from a right optic disk cut transversely to the 

 longitudinal axis of the embryo (see page .34). At r is an angle formed 

 by the growth of the retinal cells over the undifferentiated ectoderm. 

 Stage A. X 280. 



" 39. A section from the optic disk of an embryo in stage B. The plane of 

 cutting corresponds to that in Fig. 38. In this figure x indicates, as 

 in the preceding one, the angle between the undifferentiated ectoderm 

 and the growing retina, x 280. 



