STAR-FISH AND SEA-URCHINS. 305 
spines, apply equally to the pedicellariz, 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 pedicellarize, in a more marked degree. 
This applies especially to the reflex irritability of 
the pedicellariz ; 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—Ist, that the general co-ordination 
of the spines is dependent on the integrity of an 
internal nerve-plexus; 2nd, that the internal plexus 
is everywhere in intimate connection with the ex- 
ternal; and 3rd, that complete destruction of the 
former, while profoundly influencing the functions 
of the latter, nevertheless does not wholly destroy 
them. 
Professor Ewart therefore undertook carefully to 
examine the internal surface of the shell, to see 
whether any evidence of this internal nervous 
plexus could be found microscopically, and, after a 
great deal of trouble, he has succeeded in doing so. 
But as he has not yet published his results, I shall 
not forestall them further than to say that this 
internal plexus spreads all over the inside of the 
shell, and is everywhere in communication with the 
external plexus by means of fibres which pass be- 
tween the sides of the hexagonal plates of which 
the shell of the animal is composed. Thus we can 
