THE PINEAL SYSTEM OF IGUANIDA 279 



7. In adults the nerve elements are completely atrophied and only 

 the thickened perineurium remains. 



8. In one embryo of Iguana there are two parietal nerves, one from 

 each ganglion habenulee. 



III. The Proximal Pineal. 



1. At the end of the 9th day the pineal has the form of a vesicle 

 communicating with the third ventricle ; this shows a structure comparable 

 with the parietal eye vesicle. 



2. In the course of development the pineal becomes covered with cilia 

 internally and is gradually transformed into a long funnel. 



3. The proximal part of the pineal retains a structure which is 

 suggestive of that of the medullary tube ; the development of the distal 

 part resembles that of the retina of the parietal eye. 



4. The conical pineal of adult animals retains at its distal end the 

 funnel-shaped form of the embryo, while its proximal part undergoes a 

 follicular transformation during the growth of its wall. 



5. The epiphyseal evagination in the tegu shows in the early stages 

 of development, just as in Iguana, a constriction causing a division into a 

 distal part (pineal eye vesicle) and a proximal part (pineal). 



6. Later this constriction disappears and the entire primary epiphyseal 

 evagination is developed into a pineal. 



7. The pineal of the tegu, in a stage corresponding to 24-26 days of 

 Iguana, shows traces of pigmentation that appear to vanish afterwards. 



8. In an embryo of Iguana nerve bundles from the diencephalic roof, 

 entirely similar to the parietal nerve, enter the posterior part of the pineal 

 (Fig. 187, B, p. 264). 



9. On the end of the proximal pineal of one Iguana embryo and in an 

 adult a secondary pigmented pineal eye was developed. 



Among the special points which Klinckowstroem emphasizes in the 

 summary of his observations on Iguana one may note : (1) the separation 

 of the parietal vesicle, by means of a constriction from the anterior 

 part of the primary evagination ; (2) the independent formation of the 

 parietal nerve, which takes place after the separation of the eye vesicle 

 from the epiphysis ; (3) the connection of the parietal nerve with the 

 right habenular ganglion in some cases, and the demonstration in one 

 embryo of Iguana of two parietal nerves, one ending in the right habenular 

 ganglion and the other in the left habenular ganglion ; (4) the degenera- 

 tive changes in the retina and parietal nerve which occur in the late 

 stages of development, which eventually lead to a total disappearance 

 of the nerve-fibres ; (5) the distinction between (a) the proximal part 

 of the epiphysis, which undergoes a follicular transformation and an 



