ORIGIN—TASTE-BUDS OF ELASMOBRANCHS - BG 
this form reacts in the mouth and spiracle only, that is, in the 
region bearing taste-buds, as was discovered by Parker (’08) 
for the catfish. But the whole surface of the body is sensitive 
to the stimulus of sour, salty, and bitter substances. By oper- 
ations Sheldon was able to determine that these reactions of the 
general body surface are due to stimulation, not of the gustatory 
nerves which supply the taste-buds, but of the nerves of general 
sensation. ‘These same nerves of general sensation were shown 
to give rise when stimulated to responses even in the mouth, 
where also taste-buds and their nerves take part in reactions. 
From these results Sheldon concludes, and in this he agrees with 
Herrick (’08), that in the dogfish the more specialized senses 
of smell and taste (as in the taste-buds) are derived from the 
primitive general chemical sense. Parker (712), on the other 
hand, considers the olfactory sense the more primitive and 
derives from it the chemical sense which later gives rise to the 
taste-buds. 
Just how much the gustatory nerves are stimulated through 
the secretory action of the so-called sense-cells no one has ever 
been able to determine. It has, however, been suggested by 
Botezat (710) and Parker (712) that these modified epithelial 
cells to which the name taste-buds is given may be primarily 
secretory, and that the nerves receive their stimulation through 
the response (secretion) of these cells to the stimulating sub- 
stances. Materials, then, like quinine, would be tasted by the 
dogfish, because the cells of the taste-buds react to the quinine 
and secrete a substance which in turn stimulates the associated 
nerve. Such an explanation would rule out the term ‘sense-cell’ 
as applied to the groups of slender cells making up the taste-buds. 
Turning, now, to the problem of the endodermic origin of the 
taste-buds in vertebrates, we find that Johnston (’05—’10) has 
been the chief proponent of the view that they are endodermal, 
and it is he who has given the most positive and convincing 
evidence in support of this view. Johnston (’05) finds that in 
Petromyzon and two bony fishes the taste-buds develop first 
in the endodermal lining of the pharynx and make their appear- 
ance on the outer surface of the body later at the time of hatch- 
