PHYSIOLOGY OF ECUIA^ODEIIMATA. 135 



the animal, so that all the pedicels in all directions are equally 

 in contact with the sides of the vessel, the animal rights itself by- 

 rotating in some one definite direction till its oral surface is in 

 apposition with one of the sides of the beaker. 



It only remains to give a short account of the eifects of nerve- 

 poisons on the Echinodermata. 



1. Chloroform. — On mixing chloroform wnth the sea-water 

 containing Echini, the first effect was to stimulate the animals 

 to increased activity — their locomotion becoming more rapid, 

 and their spines being moved about rapidly in all directions. But 

 after a few minutes quiescence began to supervene, and increased 

 till it ended in motionless torpidity — the spines and pedicellarise 

 being all depressed, and all irritability being suspended. AVhen 

 then removed to a basin containing a large quantity of sea- 

 water without chloroform, the pedicellarise soon began to recover 

 their spontaneity, the stalks becoming erect and mobile, while the 

 forceps resumed their clasping function when stimulated by the 

 introduction of a needle between their mandibles. Next the spines 

 recovered their reflex irritability and then their spontaneity. If 

 the Echinus were inverted when restored to the normal sea-water, 

 it remained inverted for a long time, shifting its position by means 

 of its spines ; but eventually it succeeded in righting itself. 



2. Caffein. — On first immersion in a saturated solution, the 

 pedicels of Echini exhibited a curling movement, which became 

 progressively more and more languid, while they were at the 

 same time slowly but imperfectly retracted. The pedicels per- 

 sistently remained partly retracted, while both their spontaneity 

 and irritability, as also those of the spines and pedicellarise, were 

 almost completely lost. The lantern, however, continued to be 

 faintly responsive to stimulation. On replacing the animals in 

 normal sea-water, they slowly recovered their irritability, and 

 next morning were found perfectly well. 



3. Nitrite of Amyl. — The effects, when the nitrite was added 

 to the sea-water, were almost identical with those produced by 

 caffein, except that the pedicels, although motionless, were not 

 curled. On submitting an Echinus, taken out of the water and 

 placed under a bell-jar, to the vapour of the nitrite, the action 

 was more rapid. In both cases recovery became complete upon 

 restoring the animals to normal sea-water. 



4. Chloral Hydrate. — A few minutes after exposure to this 

 substance the spines of Echini fall into confusion, and the teeth 



