294« JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



Sidlon, 



1. Slar-iish. — Single rays cletacliecl from the 

 organism crawl as fast and in as determinate a 

 direction as do the entire animals. They also 

 crawl up perpendicular surfaces, and sometimes 

 away from injuries ; but the}^ do not invariably, or 

 even generally, seek to escape from the latter, as is 

 so certain to be the case with entire animals. 

 Lastly, when inverted, separated rays right them- 

 selves as quickly as do the unmutilated organisms. 



Dividing the nerve in any part of its length has 

 the effect, whether or not the ray is detached from 

 the animal, of completely destroying all physio- 

 logical continuity between the pedicels on either 

 side of the line of division. Thus, for instance, if 

 the nerve be cut across half-way up its length, the 

 row of pedicels is at once physiologically bisected, 

 one-half of the row becoming as independent of the 

 other half as it would were the whole ray divided 

 into two parts : that is to say, the distal half of the 

 row may crawl while the proximal half is retracted, 

 or vice versa; and if a drop of acid be placed on 

 either half, the serial contraction of the pedicels 

 in that half stops abruptly at the line of nerve- 

 division. As a result of tliis complete physiological 

 severance, when a detached ray so mutilated is 

 inverted, it experiences much greater difficulty in 

 righting itself than it does before the nerve is 

 divided. The line of nerve-injury lies flat upon 

 the floor of the tank, Avhile the central and distal 

 portions of the ray, i.e. the portions on either side 



