THE PINEAL BODY 85 



The white pigment of the retina. Mayer 265 in 1864 observed 

 that the epiphyseal complex in Petromyzon contained many 

 calcium bodies. Subsequently Ahlborn 2 made the observation 

 that there were a large number of small bodies of a peculiar 

 white substance which he called the white pigment and regarded 

 it as similar to the brain sand of the higher vertebrates. This 

 white substance filled in the cells of the retina in such a way as 

 to prevent the passage of transmitted light and to give the 

 appearance of a glistening white when illuminated. Accord- 

 ing to Studnicka, 388 this pigment does not appear in Ammoccetes 

 younger than those of 50 mm. in length, but thereafter gradually 

 increases in amount until the adult form is attained. Leydig 239 

 in 1896 differentiated two kinds of pigment bodies those which 

 are small in amount, of a dark brown black color and those of 

 the second type which by transmitted light appear to be a 

 brownish yellow. By direct light these pigments appear to be 

 white. 



The stalk of the pineal organ in cyclostomes. In cyclostomes 

 the pineal stalk becomes much reduced in size and it completely 

 loses its lumen in the adult. It becomes conspicuous, however, 

 by the development in it of certain nerve fibers whose collected 

 bundle was first called by Leydig 239 in 1896 the 'Zirbelnerv.' 

 This structure, later in 1898, was called by Gaupp 147 the tractus 

 pinealis and finally the nervus pinealis by Studnicka. 388 This 

 pineal nerve established a fiber connection between the peculiar 

 organ situated beneath the roof-plate and known as the pineal 

 eye in cyclostomes, and the roof of the brain. The fibrous 

 nature of its structure was first observed by Whitwell 421 in 1888. 

 Owsiannikow 295 noted that in addition to the nerve fibers there 

 were to be observed in the pineal stalk a bundle of fine nerve 

 fibers. The diameter of these fibers, according to his measure- 

 ment, was 50 micra. Running with the nerves were numerous 

 blood vessels. Gaskell 145 could not distinguish whether nerve 

 fibers or processes of cells made their course within the nerve 

 sheaths. It was only at the entrance of the nerve into the eye 

 that he found a lumen. Studnicka, 388 however, maintained that 

 the stalk was an actual nerve and therefore applied to it the term 



