i6 



THE PINEAL ORGAN 



Fig 



ct. 



Sc— ^assm — ct 



Dc-^anlnfir 1 



n Jj^^^^^^m^wm^ibAj^W^. n u 



^^^^^^^^^^^m bm 

 '"iCffift fe y ft 1 ' 



fflttlfQfiMk 



WmmmmMkk ilmmwm 



ii. — Longitudinal Section through the Optic Stalk and Eye of a 

 Crayfish (Astacus fluviatilis). (Original.) 



showing a smooth non-faceted cornea, continuous with the cuticle of the 

 stalk ; Sc. : Semper's cells partially concealed by pigment ; pc. : the 

 conical pigment caps continuous with the pigment sheath surrounding the 

 distal segments of the crystal rods cr. ; these are socketed in the cup-shaped 

 outer ends of the inner segments of these cells ; ri ., n"., n. : three zones of 

 retinal nuclei, the middle of which is obscured by pigment ; bm. : basement 

 membrane which is continuous at the margin of the retina with the basement 

 membrane beneath the hypoderm cells of the cuticle. The pedicle shows 

 four enlargements or optic ganglia, containing nerve cells, nerve fibres, a 

 reticulum of supporting fibres, the neuropil, rip. ; and spirally or transversely 

 striated, refractile spindles, sp. ; m. : insertion of muscle fibres into the hypo- 

 dermal membrane of the optic stalk ; o.sh. and i.sh., outer- and inner- 

 fibrous sheaths of the pedicle between which is a loose layer of mesenchymal 

 tissue. There is a marked spiral twist of the central nervous axis of the 

 pedicle, bv. : blood vessels ; nf. : nerve-fibres. 



