330 THE PINEAL ORGAN 



the head, in or near the surface, and they are connected by nerve-fibres 

 with a supra-oesophageal ganglion which represents the brain. Further 

 it is probable that the rudimentary eyes of this prototype animal, which 

 were at first freely exposed on the dorsal surface of the head — no carapace 

 or head-shield as yet having been evolved — as they gradually developed 



Fig. 230. — Pineal Plate of Titanichthys, from the Upper Devonian of 

 Ohio, U.S.A. (inner view, one-half natural size). Paired Pineal Pits 

 or Openings are seen in the Middle Area of Thickened Bone. (After 

 A. S. Woodward.) 



b. : radiating spicules of bone. p.p. : paired pineal impressions. 



p. pi. : pineal plate. 



into more complex organs which, with the brain and other delicate parts 

 of the head, required protection from injury, were afforded this 

 protection by the deposition of a chitinous shield around the ocelli and 

 over the surrounding soft parts, leaving a transparent epithelial or horny 



PrO 



A B 



Fig. 231. DlNICHTHYS INTERMEDIUM. 



A — Part of the roof of the skull, viewed from above. 



B — The same area, seen from the inside, and showing the parietal pit on the inner 

 aspect of the pineal plate. (After Heintz, A.) 



C. : central plate. P. : parietal or pineal plate. 



C.P. : central part. M.B. : median basal plate. 



br. : branch of central part. Pr. O. : preorbital. 



R. : rostrum. 



covering for the eyes, which became transformed into either a faceted 

 or a continuous smooth cornea. Moreover, as the type of animal became 

 more active and left the mud or sand at the bottom to swim in the water, 

 the more lateral eyes, being more suitably placed than the median eyes, 

 became more highly developed ; while the latter either retained their 



