ON THE LOCOMOTOR SYSTEM OF ECHINODERMATA. 
861 
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 spines, apply equally to the pedicel- 
larise, except that their spontaneity and reflex irritability are not destroyed, but only 
impaired. 
Some hours after the operation it usually happens that the spontaneity and reflex 
irritability of the spines return, though in a feeble degree, and also those of the 
pedicellarise, in a more marked degree. This applies especially to the reflex irritability 
of the pedicellarise; for while their spontaneity does not return in full degree, their 
reflex irritability does—or almost in full degree. 
These experiments, therefore, seem to point to the conclusions—1st, that the general 
co-ordination of the spines is dependent on the integrity of an internal nerve-plexus, 
which, however, we have not been able to detect histologically; 2nd, that the hypo¬ 
thetical internal plexus is everywhere in intimate connexion with the external;and 
3rd, that complete destruction of the former, while profoundly influencing the functions 
of the latter, nevertheless does not wholly destroy them. 
In order that a more clear conception may be rendered of the experiments on which 
these conclusions are based, we shall here quote from our notes one complete 
observation :— 
“ Echinus was divided into two hemispheres. 
“ After evisceration one hemisphere was painted over whole of internal surface with 
HN0 3 . (A.) 
“ The other was painted down one row of ambulacral plates, and also down the inter- 
ambulacral plates at another part of internal shell. (B.) 
“In (A.) the spines were ‘laid’; spontaneity and reflex irritability almost totally 
destroyed. 
“ In (B.) similar effects observed above painted areas—unpaintecl areas unimpaired. 
“ Three hours after, no considerable recovery where painted; unpainted areas as 
active as before.” 
One further point, brought out by further experiments, may here be most con¬ 
veniently mentioned ; it is that a specially great influence, or shock, seems to be 
exerted on the external plexus by injury of the hypothetical internal plexus along the 
lines of the ambulacral pores. The following observations will serve to show this :— 
“Another specimen was divided into two hemispheres. In one hemisphere two 
adjacent ambulacral rows were thoroughly scraped on internal surface of shell, and 
* It is remarkable tbat painting a portion of tbe internal surface of the shell should have the effect of 
injuring the spines and pedicellarias of the corresponding portion of the external surface; for the fact 
seems to show that there must everywhere be intimate nervous connexions passing through the calcarious 
substance of the shell. So far, however, we have not been able to detect histological evidence of such 
connexions. 
