HISTORICAL SKETCH 7 



whereas in those animals which had been kept in the dark the pigment 

 was found in the outer part of the retina, farther from the source of light. 

 The subject of the presence of pigment in and around the pineal organ is 

 of the very greatest interest with reference to (i) the origin of light- 

 perceiving organs in general (Bernard) and (2) the occurrence of regressive 

 changes and melanotic tumours in the human pineal organ. A more 

 detailed description of the position of the pigment granules, their variations 

 in type, and their significance will be given later in the appropriate places. 



Another important period in the history of the pineal body is that in 

 which its median situation between the two lateral eyes and the apparent 

 similarity of its structure to that of the median eyes of invertebrates 

 attracted the attention of some of the leading biologists and palaeontologists 

 of the time (1880-1910), more especially with reference to the light that 

 its study might shed upon the problems of the ancestry of the vertebrates 

 and the connection of the pre-vertebrate stock with that of the inverte- 

 brates. Intimately bound up with this question was the controversy 

 which arose as to whether the pineal body originated as a bilateral pair of 

 light-percipient organs or whether as two separate median organs which 

 arose serially one behind the other and belonged to two neural segments. 

 Among those specially interested in these different problems we may 

 mention : Baldwin Spencer, Lankester and Bourne, Kingsley, Beard, 

 Gaskell, Patten, Dendy, Smith Woodward, Studnicka and Klinckowstrom. 

 As in the case of pigment, the detailed consideration of these questions 

 will be most appropriately dealt with in the section on the morphology 

 of the pineal system. It may be mentioned here, however, that although 

 much speculation, based on preconceived notions and insufficient evidence, 

 occurred during this period, some of the most important observations were 

 made on the structure and nature of the pineal system during this period 

 and in some cases arose as a direct result of investigation which was 

 stimulated by the controversy. 



Among the observations brought out in this way we may specially 

 mention the discovery and accurate description of the nerves of the pineal 

 eye by Nowikoff, Beraneck, Dendy, Klinckowstrom, and others, more 

 especially in cyclostomes, fishes, amphibians, and reptiles. Moreover, 

 it will be appropriate to draw attention here to the significance of the 

 connection of the right and left pineal nerves, with the corresponding right 

 and left habenular ganglia (Dendy), and also of the relation of the pineal 

 nerves with the habenular and posterior commissures (Studnicka). We 

 may further emphasize the significance of the existence of a nervus pinealis 

 during one phase of development and the disappearance of this nerve at 

 a later stage as evidence of a regressive character being manifested in the 

 ontogenetic history of the organ. 



