The Ketina and Optic Ganglia in Decnpods, eapecially in Astacus. 71 
Fig. 35. Transverse section through the »Punktsubstauz« of the second 
= ganglion (II), a part of the first decussation {cx.l), and the sur- 
rounding ganglion cells [cl.gn). 
Fig.r 36. Transverse section through a part of the second decussation [cx.2), 
the »Punktsubstanz« of the third ganglion (III), and the surrounding 
ganglionic cells {cl.gn); x a group of especially largo ganglionic cells 
whose fibres extend from the second ganglion directly to the brain 
(cf. Fig. 59, green). 
Fig. 37. Transverse section through the fourth ganglion: its substance is 
composed of a mixture of fibres and »Punktsubstanz«. 
Plate 2. 
All figures of transverse sections are so placed that their dorsal edges are 
above, their ventral below, their anterior to the right, and their posterior to 
the left (cf. pag. 7). 
,Fig. 38. Transverse section of the optic nervo at a piane midway between the 
. fourth optic ganglion and the brain. The outlines of the individuai 
fibjres, which are usually readily distinguishable, can scarcely be made 
out in the dorsal part of the nervo [n.d). X ^^O. 
Fig. 39. Transverse section of the optic nerve of a crayfish 3 cm. long. X 
Fig. 40. Transverse section of the optic nerve of an adult crayfish. X 
Figs. 41 — 44. Transverse sections at different levels through the first ganglion. 
X 410. 
Fig. 41. Transverse section at the level of the outer nuclei (cf. Fig. 46, 2). 
Fig. 42. Transverse section at the level of the fibrous layer (cf. Fig. 46, 3). 
Fig. 43. Transverse section at the level of the inner nuclei (cf. Fig. 46, 4). 
Fig. 44. Transverse section through the »Punktsubstanz« of the first ganglion 
showing four neurommatidia. 
Fig. 45. Section from a part of the first decussation; the piane of section is 
such that some bundles of fibres are cut longitudinally, some trans- 
versely. X 410. 
Fig. 46. Section through the first optic ganglion: 1) layer of retinal fibres; 
2) outer nuclei; 3) fibrous layer; 4) inner nuclei; 5) »Punktsubstanz«; 
and 6) nerves fibres of the first decussation. A retinal fibre {fbr.r) is 
seen to form a fibrillation in the »Punktsubstanz«. yC^MQ. 
Fig. 47. A section similar to that shown in Fig. 46, but in which a fibre [fhr.n] 
from the first decussation is seen terminating in the »Punktsubstanz«. 
X410. 
Fig. 48. A nerve fibre and ganglion celi of the small type from the first decus- 
sation; the fibrillation forms a part of the »Punktsubstanz« of the 
second ganglion. Methylen blue. X ^40. 
Fig. 49. A similar fibre and celi of the largo type. Methylen blue; fixed with 
corrosive sublimate. X 140. 
Fig. 50. Fibrillation of a fibre from the second decussation and of one from 
the third decussation in the »Punktsubstanz« of the third ganglion. 
. Eapid Golgi method. X 140. 
