304 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
ducing no impairment of any of the functions of 
the pedicels, spines, cr pedicellariz), and then to 
paint with strong acid the inside of the shell—com- 
pletely washing out the acid after about a quarter 
of a minute’s exposure. The results of a number 
of experiments conducted on this method may be 
thus epitomized :— 
The effect of painting the back or inside of the 
shell with strong acid (e.g. pure HCl) is that of at 
first strongly stimulating the spines into bristling 
movements, and soon afterwards reducing them to 
a state of quiescence, in which they lie more or less 
flat, and in a peculiarly confused manner that 
closely resembles the appearance of corn when 
“laid” by the wind. The spines have now entirely 
lost both their spontaneity and their power of 
responding to a stimulus applied on the external 
surface of the shell—i.e. their local reflex excita- 
bility, or power of closing in upon a source of irri- 
tation. These effects may be produced over the 
whole external surface of the shell, by painting 
the whole of the internal surface; but if any part 
of the internal surface be left unpainted, the cor- 
responding part of the external surface remains 
uninjured. Conversely, if all the internal surface 
be left unpainted except in certain lines or patches, 
it will only be corresponding lines and patches on 
the external surface that suffer injury. It makes 
no difference whether these lines or patches be 
painted in the course of the ambulacral feet, or 
anywhere in the inter-ambulacral spaces. 
The above remarks, which have reference to the 
