THE PINEAL SYSTEM OF REPTILES 247 



which were seen by Leydig in Platydactylus lying in the stalk of the epiphysis 

 was considered by Melchers to be incorrect, the appearance of fibrillation 

 being due to the persistence of connective tissue fibres in the degenerated 

 stalk of the epiphysis. According to Klinckowstroem the tractus pinealis 

 in an 18-day embryo of Iguana tuberculata sinks into the posterior wall of 

 the epiphysis at the junction of its proximal two-thirds with the distal 



pig 



§1 



bl.v '' N n.par 



Fig. 176. — Sagittal Section through the Parietal Eye, and Parietal 

 Foramen of Varanus giganteus, showing Deposit of Pigment in the 

 Central Part of the Lens and a Division of the Parietal Nerve into 

 Two Main Branches. (After Spencer.) 



bl. v. : blood-vessel. par. 0. : parietal organ. 



/. : lens. pig. : pigment. 



n. par. : parietal nerve. r. sk. : roof of skull. 



third, and from this point to its termination in the posterior commissure 

 the tract lies free in the surrounding connective tissue. It is thus com- 

 parable with the pineal tract observed by Braem in Rana temporaria 

 (Fig. 166, Chap. 19, p. 232). Whether there is also a connection with the 

 habenular commissure or ganglia and the exact destination of the fibres 

 which enter the posterior commissure are questions which seem to be 

 unsettled. It seems probable, however, that degenerative changes similar 

 to those which occur in the parietal nerve take place and that the tract 

 disappears in late larval stages or during adult life. 



The Pineal Organ of Reptiles 



It is only in rare cases that the pineal organ of reptiles is seen to 

 consist of all three parts — end vesicle, stalk, and expanded proximal or 

 basal part, the latter of which represents the epiphysis or pineal gland 

 of birds and mammals. The end vesicle is in most cases absent, but its 



