70 
G. H. Parker 
Figs. 16 and 17, Transverse sections from the distal end of the rhabdome to 
show the peculiar W-shaped outline of this structure; Fig. 17 was 
taken from the section proximal to that from which Fig. 16 was 
drawn. 
Fig. 18. Transverse section of the proximal end of the rhabdome surrounded 
by its seven proximal retinular cells and the four fibrous prolongations 
of the cone cells. Depigmented in potassic hydrate. 
Fig. 19. Transverse section from near the distal surface of the basement mem- 
brane. The fibrous ends of the proximal retinular cells as indicated 
by their fibrillar axes (ax.n) are forming groups of threes or fours pre- 
paratory to passing through the basement membrane. The fibres be- 
longing to one ommatidium are numbered 1 to 7. The axis of each 
■ ommatidium is indicated by the slight elevation Ifbr.con) on the base- 
ment membrane where the ends of the fibres from the cone cells 
terminate. 
Fig. 20. Transverse section of groups of three and four retinal fibres immedia- 
tely proximal to the basement membrane. 
Fig. 21. Trans verse section of retinal fibres approximately halfway between the 
retina and the first optic ganglion. 
Fig. 22. Transverse section of a bundle of retinal fibres at the distai surface 
of the first optic ganglion. 
Fig. 23. Longitudinal section of a rhabdome cut in such a place that one set of 
fibrillae appear in transverse section (dots) and another set in longitu- 
dinal section (lines). Rapid Golgi method. 
Fig. 24. Transverse section of a rhabdome in which the fibrillae belonging to 
celi 2 and a few from celi 5 are colored. Rapid Golgi method. 
Fig. 25. Transverse section of a rhabdome in such a piane that some Of the 
fibrillae of both cells 1 and 7 appear. Rapid Golgi method. 
Fig. 26. Right optic stalk of Astacus cut dorsoventrally; the right side is 
ventral; the left, dorsal. X ^ö. 
Fig. 27. Right ■ optic stalk of Astacus cut anteroposteriorly ; the left side is 
anterior; the right, posterior. X 
Fig. 28. Right optic stalk of JBranchipus cut dorsoventrally; the left side is 
dorsal; the right, ventral; owing to a twisting of the stalks, the antero- 
posterior position in Astacus (Fig. 27) corresponds to the dorsoventral 
one in Branchipus (Fig. 28); x region of growth. X 
Figs. 29—33 represent pieces of corneal cuticula that were cleaned in potassic 
hydrate and studied in water. X 1^^- 
Fig. 29. Four facets from the centre of the corneal hypodermis, i. e., the 
distai pole of the optic stalk. The figure is placed as though it 
were a transverse section (see above). 
Figs. 30 — 33. Pieces of corneal cuticula from the margins of the retina: 
Fig. 30, from the dorsal margin; Fig. 31, from the posterior margin; 
Fig. 32, from the ventral margin; and Fig. 33, from the ànterior 
margin. 
Figs. 34 — 37. Transverse sections of the optic ganglia. X^S. 
Fig. 34. Transverse section through the first decussation (cf. Fig. 27), the 
surrounding ganglioriic cells [cl.gn) , and the »Punktsubstanz« of the 
first ganglion (I). 
