Johnston, TJic Bj-ain of Pctrouiyzon. 33 



latter (from the "Hirnrinde") as ending in the ganglia haben- 

 ulae, and describes other fibers from the thalamus as passing 

 through the superior commissure to end in the olfactory lobe. 

 A discussion of these tracts is reserved until after the description 

 of the fore bran, only stating here that the tractus olfacto-haben- 

 ularis are the only tracts entering the ganglia habenulae besides 

 the bundles of Meynert. The two tracts are about equal in 

 size as they enter the ventro-cephalic angles of the ganglia, 

 while the superior commissure does not appear to be much 

 larger than one tract alone. The right bundle as it enters the 

 ganglion divides into a number of bundles which make up the 

 greater part of the central fiber mass and spread into all paits 

 of the ganglion. The bundles have a general course toward 

 the middle line but decrease greatly as they approach it. The 

 larger part of the left tract goes directly to the commis- 

 sure. This disposition of the tracts indicates that the greater 

 part of both right and left tracts end in the right ganglion. 

 This is clearer than in Acipenser and the asymmetry is greater, 

 but in essentials the two forms agree. 



Unfortunately there is no impregnation of fibers or cells 

 in the epiphysis or Zirbelposter and I can give only a few ob- 

 servations on haematoxylin sections. The general relations of 

 these structures have been described above. The extremely 

 attenuated stalk of the epiphysis is too small to contain any 

 considerable number of fibers. No fibers are to be seen in 

 haematoxylin sections and, indeed, in some preparations the 

 stalk seems to be completely obliterated in its caudal part. The 

 tract which F. Mayer ('97) figures as running to the posterior 

 commissure is impossible in Lampetra. The epiphysis itself is 

 a vesicle whose cavity is largely obliterated by the thickening 

 of its walls. The ventral wall is considerably thickened in two 

 longitudinal ridges, one at either side of the hollow stalk. This 

 wall is composed of a single layer of columnar cells which are 

 higher in these two ridges. Among the bases of these cells 

 are a few stellate cells having the appearance of nerve cells as 

 Studnicka ('00) describes. The nuclei of the epiphysis cells 

 have taken a distinct chromatic stain in iron haematoxylin. In 



