578 Proceedings of Royal Society of Edinburgh. [sess. 
17) in Fishes. In this connection it is also interesting to note 
that Locy (19) describes the epiphysis of Elasmobranchs as 
developing from a pair of united accessory optic vesicles, while in 
Ammocoetes, Gaskell (12) has shown the presence of a right and 
a left pineal structure. As a result both of the observations of 
these workers and of the present research on the Amphibia, it is 
to be noted that in the three lower Vertebrate classes the 
epiphysis arises as a bilateral structure, and not as a mesial un- 
paired structure. 
5. As already stated by Dendy (9), “the ancestors of Verte- 
brates must have possessed a pair of parietal eyes, which may 
have been serially homologous with the ordinary Vertebrate 
eyes.” 
IV. Literature. 
The following is a list of the papers bearing upon the present 
research, which the author has had an opportunity of consulting : — 
(1) Balfour, F. M., Comparative Embryology , vol. ii., 1881, 
p. 418. 
(2) Beard, J., “The Parietal Eye in Fishes,” Nature , vol. 
xxxvi., 1887, pp. 246 and 340. 
(3) Beard, J., “Morphological Studies. — I. The Parietal Eye of 
the Cyclostome Fishes,” Quart. Jour. Micr. Sci., vol. xxix., p. 55. 
(4) Beraneck, E., “Parietal Eye and Nerve,” Abstract in the 
Jour, of the Roy. Micr. Soc., 1892, p. 761. 
(5) Bernard, H. M., “An Attempt to deduce the Vertebrate 
Eyes from the Skin,” Quart. Jour. Micr. Sci., vol. xxxix., 1897, 
p. 343. 
(6) Burckhardt, B., “ Die Homologien des Zwischenhirndaches 
und ihre Bedeutung fur die Morphologie des Hirns bei nie deren 
Vertebraten,” Anatom. Anzeiger , Bd. ix., 1894, p. 152. 
(7) Burckhardt, Pi., “ Die Homologien des Zwischenhirndaches 
bei Beptilien und Vogeln,” Anat. Anz., Bd. ix., 1894, p. 320. 
(8) Burckhardt, B., “Der Bauplan des Wirbelthiergehirns,” 
Morpholog. Arbeit., 1894, Bd. iv. p. 131. 
(9) Dendy, A., “ On the Development of the Parietal Eye and 
adjacent Organs in Sphenodon (Hatteria),” Quart. Jour. Micr. Sci., 
vol. xlii., 1899, p. 111. 
