48 Journal of Comparative Neurology. 



developed into the tela choroidea. This latter does not begin 

 to appear behind, until a little later and that at first in the form 

 of two simple elongated folds reaching to the sides of the in- 

 ferior organ. The only place where it unites with the brain is 

 at its posterior extremity where it is attached from above to the 

 anterior extremity of the left habenular ganglion. The organ 

 unites also in part with the right habenular ganglion as already 

 remarked. Our author finds the union with the ganglion in the 

 same sections of the series in which the pineal organ joins the 

 ganglion. At the juncture of the organ with the ganglia the 

 latter are found closely associated and touching each other. Im- 

 mediately behind this place we see in the following sections ner- 

 vous filaments passing from one into the other ; this is the 

 supra-commissure. Here our author remarks that it is an inter- 

 esting fact that the epiphysis takes its origin in front of the post- 

 commissure and the parapineal organ in front of the supra-com- 

 missure. The form of the parapineal organ resembles, in this 

 stage, that of the pineal organ. Its anterior extremity ends 

 almost in a point. The walls at this extremity are thin and 

 composed of a single layer of cells. Farther caudad the inferior 

 wall is much more developed and is thicker than the superior 

 wall. What has been said of the form of the organ in larvae 

 27 mm. long, applies also to its form in the adult fishes. The 

 union of the organ with the right ganglion very soon suffers in- 

 terruption, whereas that of the left remains. In longitudinal 

 section it is attached to the anterior extremity and prolonged 

 from the left habenular ganglion. In the case of more devel- 

 oped Ammoccetes this ganglion is still more prolonged and the 

 organ pushed farther forward. The prolongation is made so 

 that the more anterior part of the ganglion (Zirbelpolster, Ahl- 

 born) is separated from the posterior part and does not remain 

 connected with it. It is composed of a little bundle of nervous 

 filaments. This little bundle is later prolonged and transformed 

 into a slight nervous bundle. In case of the adult Petromyzon 

 this commissure is very long and is recurved in the form of a 

 semicircle. In the transverse section of this nervous juncture 

 we find it very much flattened. It is more so in the older 



