258 TTVEL [VoL. IX. 
the anterior. The primitive mode of origin remains to be 
determined. 
6. The cell structure of the vesicles in the early stages is 
the same in Teleosts that it is in Lacertilia. In both groups 
the walls of each vesicle are made up of a number of layers of 
rounded cells, and are consequently distinguished from the 
adjacent brain-wall by their greater thickness. 
c. If we compare the anterior vesicle in Teleosts with the 
anterior vesicle in Lacertilia, we find that in both groups it very 
early loses its connection with the brain-roof. In Lacertilia, 
after this connection is severed, the vesicle passes cephalad, 
soon takes the form of an eye, and ultimately comes to 
lie dorsal to the cerebrum just beneath the integument. In 
Teleosts it does not pass cephalad, but remains throughout life 
embedded between the walls of the thalamencephalon and the 
mesencephalon, close against the stalk of the epiphysis, and 
never reaches an eye-like structure. 
d. If we compare the posterior epiphysial vesicle in the two 
groups, we find the embryological history identical. In the 
adults of both groups its distal part is turned cephalad, and is 
very much enlarged, while its proximal part is narrow and 
cylindrical. The minute structure of the posterior vesicle or 
epiphysis has not received from morphologists the attention 
that has been devoted to the parietal eye. Hoffmann (’s8) says 
that cylindrical cells, nerve-fibres and ganglion cells are present 
in the epiphysis of Hatteria, while Leydig (90) finds (in 
Lacertilia) an inner row of columnar cells, and outside of this 
several layers of round nuclei without distinct cell boundaries. 
The two sorts of cells recognized by Hoffmann and Leydig 
suggest a comparison with the nerve-cells and non-nervous 
cells of the Teleost epiphysis. There is a further resemblance 
in the fact that in both Teleosts and Lacertilia the epiphysis 
takes on intimate relations to the blood-vessels. 
In view of the resemblance noted above, tt seems to me that 
the two epiphysial vesicles tn Teleosts are homologous to the 
corresponding structures in Lacertilia, the antertor vesicle to the 
Lacertilian parietal eye, and the posterior vesicle to the Lacer- 
tilian epiphysis. Vf this is true, then the probability that in 
