THE PINEAL BODY OF THE SHEEP 257 



about a year the body is approximately spherical with a diameter 

 of about 3 mm. In youth the body is largest (ca. 7 mm. x 5 mm.) . 

 The pineal bodies of old individuals are considerably smaller. 



The presence of so great an amount of melanic granules as to 

 discolor the entire body at about half term, indicates that the 

 secretory activity of the 'gland' may be greatest at this stage of 

 development. But the granules are only relatively more abun- 

 dant at this stage, being elaborated more abundantly by individ- 

 ual cells. Subsequently the protoplasmic energy seems directed 

 towards cell proliferation. In consequence, the total amount of 

 granules is distributed among a larger munber of cells, each with 

 fewer granules. The entire bulk, however, has remained about 

 the same or possibly slightly increased by small additions, to the 

 time of birth. Thereafter the granules seem actually to disap- 

 pear in great part. 



The iodine test for glycogen was negative. Nor could chromaf- 

 fine granules be detected. The pineal body can therefore not be 

 regarded as a portion of the so-called 'chromaffine system' nor 

 as ganglionic in character. The histologic features of the pineal 

 body correspond more closely to those of a gland than to any other 

 structure. Its great vascularity, blind acini (cysts), and cyto- 

 plasmic granules mark it as a ductless gland. 



Weigert-Pal preparations reveal the presence of a bundle of 

 medullated nerve fibers in the proximo-ventral portion of the gland, 

 continuous with the fibers of the posterior commissure. A still 

 more delicate bundle passes from the superior commissure into the 

 proximo-dorsal portion. This may represent the so-called 'pineal 

 nerve.' The final terminations could not be determined. Both 

 in the basal portion and in connection with the blood-vessels oc- 

 casional delicate fibers could be identified. Methylene blue 

 preparations of fresh tissue (from extirpation experiments) and 

 Cajal and Golgi preparations reveal the presence of still more 

 delicate non-medullated fibers. It could not be determined 

 whether the latter are simply the naked axis-cylinder termina- 

 tions of the former. Nor can I elucidate the matter of nerve ter- 

 minations in the parenchyma of the pineal gland. The striking 

 fact that these preparations show, however, is the apparent scar- 



