1878. ] = The Sensory Organs. 587 
also carry hairs which extend beyond the epithelial surface, as in 
the ear. They serve probably as tactile organs of the most deli- 
cate character in order to take note of movements of the water 
which would not be appreciated by ordinary organs of touch.” 
In man the character of the medium in which he lives and the 
dryness of the epithelium, would seem to forbid such a structure, 
yet it becomes a very interesting question whether in mammals in 
which the necessary external conditions are present such a struc- 
ture reappears. Indeed, our interest is perhaps augmented when 
we find that Camper, about 1822; discovered innumerable open- 
ings on the lower jaw of the whale, which were like the mucous 
canals of the pike. Concerning their structure and even their 
presence in other Cetaceans nothing is known. 
There are certain great facts of embryology - which ` might 
almost lead us to suspect from an “a priori” point of view some 
bond of union between sensory organs. In the first place, the 
nerve epithelium of the ear, the olfactory region and the taste- 
buds, are developed from one and the same layer, namely, the 
epiblast of the embryo. Again this layer is the same as that 
from which the central nervous system is developed, and this fact 
alone would naturally lead us to look for the ultimate sensory 
apparatus in the epithelium. These organs being developed in fhe 
same layer, we might expect to find some morphological connec- 
tion or relation between them. The ear, as we know, is formed 
by an inflexion of the epiblast, while the nasal and oral cavities 
‘are lined by the same layer. Therefore, if,as we have seen, there 
are sensory cells in the epithelium covering the body, the cavities 
formed by the inflexion of this epithelium would contain these 
sensory cells. 
For the ear, even additional evidence is furnished by the Savian 
vesicles of the torpedo, These are closed fibrous capsules, con- 
taining an interior granular substance, and supplied by a nerve 
twig. They are arranged in linear series bordering the anterior 
_ part of the mouth and nostrils, and extending over the surface of 
the fore part of the electrical organs (Owen, Comp. Anat.; and Boll 
M. A. 1875). Max Schultze was the first to investigate the his- 
tology of these organs. He tells us that they contain an epithelium 
bearing stiff, non-vibratile hairs, and he expresses the opinion that 
the nerves bear the same relation to it as in the ear, nasal m. m. : 
etc. Boll (M. A. 1875) re-investigated the Savian vesicles and 
