Sorensen, Study of Epiphysis and Roof of Diencephalon. 47 



The proximal part of the stalk is attenuated to a diameter of 

 .009 mm., while the distal part nearest the organ containing the 

 opening has a diameter of .03 mm. From its resemblance in 

 development to the optic nerve and from its histological struct- 

 ure Studnicka gives to the stalk the name nerve ; and as it be- 

 longs to the pineal organ he calls it the pineal nerve. Further 

 this author observes that the pineal organ attaches itself ob- 

 liquely to the ganglion of the left habena and also to the side of 

 the right habena, uniting again with the latter at a point on the 

 posterior part. . The importance of this secondary reunion he 

 does not indicate. The nervous filaments have not been traced 

 from the ganglion into the organ, nor are ganglionic cells found 

 in this part. In the case of younger embryos of 23 mm. long 

 preserved in Miiller's fluid, the pineal organ is completely de- 

 tached. The reunion with the right habenular ganglion has not 

 yet occurred, or possibly is already interrupted. This larva 

 although smaller is apparently more developed. The reunion 

 was already found in larvae 7 mm. long. In case of 

 other larvae, although better formed, it is not yet found. The 

 stalk is free, not reunited with the ganglion as in the case of 

 those described above. In this example the reunion has been 

 premature, being produced normally in larvae 10 mm. long. 



The Parapineal Organ. The origin of the parapineal or- 

 gan was not found by Studnicka, as the vesicle was completely 

 closed. In case of the youngest Ammoccetes studied (23 mm. 

 long) the organ was laterally situated. Its walls were thin and 

 it had a large cavity. In sections of larvae 26 mm. long the 

 parapineal organ was found to be no more developed than in 

 larvae 23 mm. long. The organ was found under the pineal 

 organ which was a little inclined to the left but not so much as 

 in larvae 23 mm. long. The posterior portion is more lateral 

 than the anterior as in the case of the pineal organ. The para- 

 pineal organ is not attached closely to the pineal organ, there 

 being a narrow section of connective tissue with small nuclei 

 between them. This tissue belongs without doubt to the cere- 

 bral coats. It is attached below to the superior walls of the 

 thalamus. The anterior portion of this wall is thin but is not 



