58 Journal of Comparative Neurology. 



whether they unite with it. The parapineal organ is innervated 

 from the left habenular ganglion. The branch of the left bundle 

 of Meynert also enters here. 



Klinkowstrom (.^-'93) gives the following summary : 



I. Parietal eye. 



1. The pineal eye of Iguana, arising from the constriction 

 of the distal part of the primary epiphysial evagination appears 

 on the ninth day as an oval vesicle more or less constricted off 

 from the proximal epiphysis. 



2. The originally strongly biconvex lens in the course of 

 development takes a fiat slightly biconvex or even plainly con- 

 vex form. 



3. From the 14th to the 18th days the entire inner side of 

 the eye-cavity is covered with cilia. A strong nerve unites the 

 under side of the eye-vesicle with the roof of the diencephalon. 

 The retina shows two zones, one inner, without cells and an 

 outer, cellular zone. Black pigment begins to appear on the 

 retinal cells, and from the surrounding mesoderm, a connective 

 tissue capsule surrounding the nerve and eye begins to be 

 formed. 



4. In 24 to 26 days the parietal nerve has reached its high- 

 est development. Through the inward (?) growth of the nerve- 

 fibres the retina is divided into an outer and inner cell layer, be- 

 tween which the nerve can be seen as a thin fibre-layer. In the 

 inner zone an abundance of pigment has been formed. 



5. In 35 to 40 days the nerve and nerve-fibre layer show 

 significant signs of degeneration. The pigment has largely 

 increased. 



6. In the adult Iguana the pineal eye shows the variations 

 characteristic of rudimentary organs. 



7. The nervous elements appear to have entirely disap- 

 peared in the retina and the formation of pigment has become 

 so excessive that a recognition of the structural relations is often 

 impossible. 



II. The parietal nerve. 



I. The nerve which enters the pineal eye is not similar in 

 its development to the optic nerves of the paired eyes. 



