STAR-FISH AND SEA-URCHINS. 305 



spines, apply equally to the pedlcellarire, except 

 that their s[)ontaneity and reiiex irritability are not 

 destroyed, but only impaired. 



Some hours alter the operation it usually happens 

 that the spontaneity and reiiex irritability of the 

 spines return, though in a feeble degree, and also 

 those of the pedicellari^B, 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 

 docs — or almost in full degree. 



These experiments, therefore, seem to point to 

 the conclusions — 1st, that the o'eneral co-ordination 

 of the spines is dependent on the integrity of an 

 internal nerve-plexus ; 2nd, tiiat the internal plexus 

 is everywhere in intimate connection with the ex- 

 ternal; and ord, 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 tlie sides of the hexagonal plates of which 

 the shell of the animal is composed. Thus we can 



