80 THE PINEAL ORGAN 



The pigmentation of the lateral eyes in lower types of vertebrates 

 does not vary in any essential manner from that in the human eye. In 

 all cases, whether in the choroid or in the retina, we find the same kind 

 of deep coloured pigment (melanin), which when viewed en masse in thick 

 sections appears black. In making a comparison of this actively functional 

 dark pigment in eyes which when in use are exposed to bright light with 

 the pigment of the pineal body (basal epiphysis) which in the higher types 

 of vertebrates is enclosed in the cranial cavity and is never exposed to 

 light, one may note, as has been pointed out by Quast, that the pigment 

 found in the parenchymal cells is of a yellow-brown colour and resembles 

 the type of pigment which is found in degenerating nerve cells either in 

 disease or in advanced age. Where the pigment is darker in colour, as 

 in the membranes and in the supporting tissue, the explanation is probably 

 to be found in the nature of the blood supply, which like that of the 

 suprarenal body approaches the sinusoidal type. It may be assumed 

 that owing to a slowing down of the circulation, any chromatophores or 

 pigment-producing substances would tend to be deposited either in the 

 meshes of the reticulum or in the substance of the cells. The deposit 

 of dark pigment in the retina of the parietal organ is obviously an hereditary 

 condition. 



