1894.] Zoology. 433 
Descartes assigned as a proper sized organ for the residence of the soul, 
this structure was first pointed out by de Graaf and Spencer, almost 
simultaneously, as a veritable visual organ in process of disappearance. 
After their papers the literature of the organ grew rapidly until the 
veteran histologist, Leydig, announced that it was not an eye; and 
since he had been the first to suggest that the structure was sensory 
his final dictum, finely illustrated, naturally had weight. Then Ber- 
anek showed that there were two organs confused, an anterior eye and 
a posterior vascular or glandular structure. The two recent papers to 
which we have referred throw no little light upon the matter. Prof. 
W. A. Locy has described’ the early phases of the eye in the Sela-. 
chians and he further shows that the early optic pits are but one of 
three serially homologous pairs of structures which differ in their early 
stages only in the matter of size. The posterior pairs are traced 
into the optic outgrowth. In the second paper Klinckowstrém® 
gives a number of facts regarding the structure of the parietal organs 
in the South American Iguana and Tejus which in connection with the 
work of Locy and Beranek tempt one to indulge in speculation. 
With what Klinckowstrém has to say of the parietal eye proper we 
have little to do. It is rather with the secondary structures. There 
are in Iguana two distinct phases to the epiphysial outgrowth. In the 
first the parietal eye proper is cut off from its connection with the 
cerebral cavity thus forming the eye and the epiphysis. Next, the 
distal portion of the epiphysis takes on a histological character closely 
approaching that of the parietal eye, the deeper portion retaining its. 
former conditions, and a constriction tends to separate this from the 
rest. Klinckowstrém naturally considers this as the temporary 
appearance of a second epiphysial eye. In connection with Locy’s 
observations and especially when taken in connection with Klinckow- 
strém’s further observation that there is a second nerve developed in 
position for this outgrowth, the conclusion is inevitable that the ances- 
tor of the vertebrates had not three eyes but at least three pairs of 
eyes. As is well known the parietal nerve is not median but on one 
side. In some cases he found one on either side, showing that the lack 
of symmetry is due to a failure to develop on the part of one of the | 
nerves. One of Klinckowstrém’s conclusions seemsa little questiona- 
ble. He concludes that the parietal nerve is not strictly comparable 
to the optic nerve, the point apparently being that in the one case tha 
nerve follows the optic outgrowth while the parietal nerve does not, 
‘Jour, Morphol. IX, 115, 1894. See also Anat. Anzeiger. 
‘Zool. i Abth. Anat. VII, 249, 1894. 
