2y2 THE PINEAL ORGAN 



Geckonidae. 



In the geckos no parietal organ is developed and the pineal organ 

 consists of a long, tubular outgrowth springing from the usual site 

 between the habenular and posterior commissures and passing upwards to 

 the roof of the skull behind a well-developed dorsal sac and paraphysis. 

 In a 31-mm. embryo of Gehyra oceanica, described by Stemmler, the base 

 of the outgrowth is constricted so as to form a secondary stalk in which 

 the lumen has become obliterated and the distal end is slightly expanded 

 into an end vesicle, the tip of which is prolonged forward as a beak-like 

 process ; this is connected to the dura mater of the skull roof by a fibrous 

 cord. The lumen of the end vesicle is smooth, there being no folds or 

 lobulation. The conditions are, therefore, very similar to those which 

 are found in the tubular type of pineal system present in the Selachia. In 

 older specimens, e.g. Hemidactylus verruculatus, brown pigment has been 

 observed in the epithelium of the distal end of the epiphysis (Ley dig). 

 The same author described in Platydactylus muralis fine striated strands in 

 the stalk of the epiphysis near the posterior commissure, which he was 

 inclined to believe were nerve-fibres passing from the posterior commissure 

 into the epiphysis. The existence of a true pineal nerve in geckos, 

 however, appears to be very doubtful, and in certain specimens, e.g. 

 Hemidactylus mabouia, it has been definitely stated that it could not be 

 demonstrated. 



The epiphysis in older embryonic specimens may show a certain degree 

 of differentiation with thickening of its wall ; in late stages of develop- 

 ment and in mature animals kinking and irregularity of the wall has 

 been present, accompanied by penetration of vessels. The epiphysis 

 has, moreover, been found separated from the roof of the brain, presumably 

 by constriction of its stalk, attended by loss of its lumen and final rupture, 

 as in the case published by Melchers in 1899. 



The changes which have been observed in the late stages of development 

 of the epiphysis of geckos include : elongation of the cells ; disappearance 

 of cell contours ; vacuolation of cellular bands ; penetration of blood- 

 vessels ; deposit of pigment in and around the capsule and the separation 

 of the whole organ from its connection with the roof of the brain. Taken 

 together, and more particularly the complete severance of the epiphysis 

 from the central nervous system, these changes indicate that the epiphysis 

 in the mature animal shows indubitable signs of retrogression. 



Agamidae. 



This family includes lizards of widely varying types. One of the 

 most remarkable is the little flying dragon Draco volans, in which the 

 hinder ribs are expanded and covered by a thin membrane ; this forms a 



