STRUCTURE OF THE PINEAL ORGAN OF REPTILES 249 



the epithelium of the accessory organ and its location in the proximal 

 segment of the accessory vesicle, or when continuity with the end vesicle 

 of the pineal organ is preserved, its attachment to the distal extremity 

 of this, form in our opinion, important evidence in favour of the accessory 

 organ being the vestige of a light-percipient organ and of its homology 

 with the parietal sense organ. 



Structure of the Pineal Organ of Reptiles 



The microscopic structure of the wall of the pineal sac of an adult 

 Sphenodon is shown in Fig. 178, after Dendy. The appearances are very 



mmw 



wuiw 



n Sx m^mm^ 





-b m 



Fig. 178. — Part of a Longitudinal Vertical Section through the Wall of 

 the Pineal Sac of an Adult Male Sphenodon (after Dendy), showing 

 details of Microscopic Structure, which closely resemble those of the 

 Pineal Eye (Fig. 181). 



b.m. : basement membrane. l.n.f.s. : layer of nerve-fibres of pineal sac. 



B.V. : blood-vessel. m.l.i. : membrana limitans interna. 



g.c. : ganglion cell. p.m. : pia mater. 



haw. : hsematid. r.f. : radial fibres. 



hue. : leucocyte. s.c. : sensory cells. 



similar to those seen in the retina of the parietal organ, but there is in 

 most specimens a lack of pigment in the inner epithelial layer and of large 



