THE OPTIC VESICLES OF ELASMOBRANCHS AND 
THEIR, SERIAL RELATION TFOLOGMER STRUCT 
URES: ON THE: CEPHALIC. PEALE: 
WILLIAM A. LOCY. 
THE evidence is increasing that the different organs of 
special sensation in vertebrates all belong to one series and 
are modifications of a sensory basis of common origin. 
The derivation of the ears from the organs of the lateral line 
system, seems now to be established ;!_ but the relationship of 
the eyes is still obscure, and they are not commonly admitted 
to the same group with the ears and other serial sense organs. 
The fact that the eyes spring from epithelium of the neural 
plate, while the other serial sense organs have, presumably, 
an independent epiblastic origin, is regarded by many as 
sufficient evidence that the eyes belong to a different series 
and cannot be identified with the other sense organs. At 
the present time, I think most morphologists would not feel 
warranted in going further than to assume the possibility of 
the eyes belonging to the same class with the other ganglionic 
sense organs. 
Froriep,” in 1885, published the researches from which the 
modern views on the relation of sense organs take their 
departure, and Beard® almost simultaneously published the 
results of his studies on the sense organs, giving the name 
“Branchial sense organ” to certain ones located just above 
the branchial region. Beard, in another paper, is especially 
strenuous against admitting the eyes into the same category 
with the ears and organs of the lateral line system. 
The writers who have since touched upon the question, 
opened up by the researches of Froriep and Beard, are very 
1 Ayers, A Contribution to the Morphology of the Vertebrate Ear, etc., 
Journ. Morph., Vol. 6, Nos. 1 and 2, May, 1892. 
2 Froriep, His. Archiv., 1885. 
8 Beard, Quar. Journ. Mic. Sci., November, 1885. 
