BRANOCHIAL SENSE ORGANS IN ICHTHYOPSIDA. 141 
our disposal, we cannot decide, and can only suspect that such 
was once the case from the relationship of the other branchial 
sense organs to gill-clefts, and from the known facts that cer- 
tainly Vertebrates once possessed more clefts than at present. 
At any rate, at present the thymus or thyroid of the nose and 
ear, or their equivalents, have still to be found. 
The only zoologists who have suggested a different view of 
their nature are Froriep and Blaue, who have suggested that 
the ear is a gill-cleft. Apart from the evidence given in the 
preceding pages, which is inconsistent with this view, one may 
reasonably ask that the supporters of such a view shall give us 
more evidence than that afforded by an epiblastic depression 
that an organ is a gill-cleft. 
In this matter the nose and ear stand on equal terms, and 
until we have a few more of the structures which compose a 
gill-cleft and visceral arch, such as arterial arch, cartilage, &c., 
assigned to them, we can reasonably regard the matter with a 
certain amout of reserve. 
It is interesting to notice that if my views be correct the 
nose and ear are the only remains of the branchial sense 
organs! in the adults of higher Vertebrates. They have sur- 
vived with a possible change of function, while the other 
branchial sense organs have disappeared except in the first 
stages of the embryo, and are then only transitory structures. 
Tur MorpHoLocy oF THE SUPRABRANCHIAL NERVES. 
This point has, I think, been sufficiently demonstrated in 
the general part of this work. The supra-branchial nerves are 
merely concerned in extensions of the branchial sense organs to 
a distance from the ganglia. They are erroneously called dorsal, 
for this condition when acquired is purely secondary. 
Any commissural nature of some of these branches, as sug- 
gested by Marshall and Spencer, is out of question. None of 
’ Professor F. H. Schultze notwithstanding, the possibility that the taste buds 
of the tongue of higher Vertebrates are also to be referred to those sense 
organs must be borne in mind. Their innervation by the glossopharyngeal is, 
in this connection, very suggestive. 
