THE PINEAL BODY 



81 



certain parts, as for example, a dorsal wall and a ventral wall, 

 which are to be distinguished from each other by certain histo- 

 logical features. These two walls bound a cavity or lumen 

 concerning which there has been much discussion and to which 

 the name of atrium is usually applied. Ahlborn 2 in 1883 states 

 that this atrium presents a peculiar lacunar appearance. 



Fig. 45 Cross section of the epiphyseal complex in Petromyzon, according to 

 Ahlborn, 1883. 



Po., pineal organ; Ds., dorsal sac; Pp., parapineal organ; Ha., habenular 

 ganglion. 



Beard 18 in 1889 thought the atrium contained a coagulated 

 fluid, and Owsiannikow 295 in 1888 was of the same opinion. 

 Gaskell, 145 however, in 1890 found that the atrium of the pineal 

 organ in Ammocoetes was in reality filled with cellular tissue 

 and, according to this observer, the pineal organ in these forms 

 had a general structure which was similar to the composite 

 eye of Arthropods. Leydig 239 in 1896 found the atrium filled 

 with what he calls secretory fibers extending inward from the 

 retinal cells of the organ. Studnicka 384 in the later stages of 

 Ammocoetes found in the lumen of the end-vesicle a peculiar, 



MEMOIR NO. 9 



