262 H. E. JORDAN 



Dimitrova ('01) gives an excellent review of the earlier liter- 

 ature on the mammalian pineal organ. She credits Cionini 

 ('88) with having first demonstrated the neurogha nature of the 

 pineal body. Galeotti ('96) appears to have been among the first 

 to argue cogently for a secretory function of the pineal organ. 

 According to Galeotti the cells of the parenchyma elaborate pig- 

 ment and, by a different mechanism, a product of secretion in the 

 formation of which nucleus and nucleolus participate. He also 

 seems first to have suggested that the pineal body is predomi- 

 nantly neuroglia in nature, the several parenchymal elements 

 being variously modified ependymal cells. This is also Dimi- 

 trova's conclusion, in opposition to that of previous investigators 

 who recognized in the parenchyma two or three specific types of 

 cells. 



Dimitrova describes cavities lined by cylindrical cells in ox, 

 calf, sheep, and dog. Both the cytoplasm and the nuclei of the 

 parenchymal cells are said to contain granules. Dimitrova does 

 not attempt to decide as to whether they have a secretory signi- 

 ficance or whether they build neuroglia fibers, or whether they 

 represent degeneration products. She describes nerve fibers in 

 relation to the blood-vessels ; but was unable in the adult to recog- 

 nize them with certainty in the parenchyma ''among innumerable 

 fibers which impregnate with silver chromate." Nor can she 

 confirm Cajal's observation concerning the presence of sympa- 

 thetic cells. 



In Oppel's Lehrbuch, Studnicka ('05) gives a masterly brief 

 summary of our knowledge regarding the structure of the mamma- 

 lian pineal body. The appended bibhography includes a complete 

 list of the literature on the vertebrate pineal organ. 



NATURE OF THE CYTOPLASMIC GRANULES 



The sole granular elements of the cytoplasm that I have been 

 able to demonstrate with the aid of all the different technical 

 methods above mentioned, are equally well discernible in un- 

 stained preparations of formalin-fixed material. They have a 

 uniform spherical shape but vary considerably in size, the larger 

 being approximately ten times the bulk of the smallest (fig. 4 b). 



