TACTILE RESPONSES OF DE-EYED HAMLET 73 
rarily broken down, to a certain extent, so that substances nor- 
mally kept apart are free to intermix and react. There is no 
reason to expect that the products of the chemiéal activation of 
epithelial cells should be able to bring about a specific action 
upon tactile nerve endings or upon the specialized accessory end 
organs of the tactile sense. ‘Tactile organs, ‘corpuscles,’ or what 
not may obviously be (and in fact frequently are) situated at 
some distance from the outer epithelial surface; it is probable, 
however, that the ‘epicritic’ form of irritability described in the 
hamlet depends upon very superficial structures; hence their 
particular value for the present research. 
These considerations may enable one to see why it would be 
somewhat surprising to find tactile organs in fishes capable of 
being normally excited by acids, for example. 
It is easily seen that differential anaesthesia is, by itself, in 
many cases a poor criterion of sensory differentiation; and yet, in 
the case of cocaine, when the results obtained by this method 
agree perfectly with other and quite independent methods of analy- 
sis, the results must perforce be accepted. In the present case 
it is rendered probable that the production of stimulation by 
chemical irritants applied to the general surface of Epinephelus 
has nothing to do with tactile receptors, and that the oblitera- 
tion of tactile (‘epicritic’) sensitivity by cocaine is not an “arti- 
fact’ due to the specifically more intense action of the chemical 
irritants. Even in coelenterates there are indications that irri- 
tant chemicals and mechanical agencies respectively act in a 
sensory way upon differentiated receptors having diverse inter- 
nal connections (Parker, ’17), and the present observations con- 
firm the idea that these agencies have modes of action in lower 
vertebrates as separate as they are in man. 
4. Responses similar to those described for the de-eyed ham- 
let are exhibited by the normally blind cave fishes, according to 
- Eigenmann (cited by Whitman, ’99, p. 303). The parallelism 
is striking, since in both cases the direction from which a rod is 
being brought near is accurately located, while vibrations of a 
coarser order may not be responded to. Inthe blind fishes, how- 
ever, this form of sensitivity is said to be more active in younger 
individuals than in adults. 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 2 
