292 John H. Welsh 



Preliminary autotomy experiments soon showed that H. nudus differed significantly 

 from U. mordax. The legs of Hemigrapsus usually had to be crushed with heavy 

 forceps to induce autotomy and, after the injection of extracts or drugs, there was no 

 graded response to be seen in the per cent of legs autotomized. However, it was noted 

 that Metridium tentacle extract induced spontaneous autotomy of both chelae and 

 walking legs, and the frequency of autotomy was related to dose. The results of a 

 typical experiment are given in Table III. Such a table does not reveal the true nature 

 of the response. In order to do this, the protocol of a typical experiment follows: 



July 30, Metridium tentacle extract number 3 (=M-3) 



4.25 p.m. Injected 10 H. nudus with 005 ml M-3, 1 :1 with sea water. 



4.30 p.m. 17 walking legs and 6 chelae had been spontaneously autotomized. Crabs are 



paralyzed and fail to right themselves when turned on their backs. 

 8.00 p.m. All crabs dead. 



4.55 p.m. Injected 10 H. nudus with 005 ml of M-3, diluted 1 :10 with sea water. 

 5.00 p.m. 18 walking legs and 10 chelae autotomized; crabs paralyzed. 

 8.00 p.m. All dead. 



5.08 p.m. Injected 10 H. nudus with 005 ml of M-3, diluted 1 :20 with sea water. 

 5.15 p.m. 30 walking legs and 11 chelae autotomized; crabs slightly paralyzed. 

 8.00 p.m. All apparently dead. 



5.23 p.m. Injected 10 H. nudus with 005 ml of M-3, diluted 1 :40 with sea water. 

 5.28 p.m. 21 walking legs and 8 chelae autotomized; crabs appear normal. 

 8.00 p.m. 3 crabs living but paralyzed. 



5.35 p.m. Injected 10 H. nudus with 05 ml M-3 diluted 1 :80 with sea water. 

 5.40 p.m. 6 walking legs and 2 chelae autotomized ; crabs appear normal. 

 8.00 p.m. 3 crabs living but paralyzed. 



5.45 p.m. Injected 10 H. nudus with 005 ml M-3 diluted 1 :150. 



5.50 p.m. 3 walking legs and 1 chela autotomized. 



8.00 p.m. 9 crabs living but partly paralyzed; few can turn over when placed on backs. 



When extracts of Cyanea tentacles were injected into H. nudus, spontaneous auto- 

 tomies rarely occurred at any of the dilutions. With dilutions up to 1 :50, paralysis 

 occurred, but it was, if anything, less severe than with equivalent amounts oi Metridium 

 extract. 



It will be recalled that tetramethylammonium chloride (Me4N), like tentacle extracts, 

 facilitated autotomy in U. mordax. When Me4N was injected into H. nudus, even in 

 high concentration, it seldom produced spontaneous autotomy, and reduced somewhat 

 the tendency of stimulated legs to autotomize. While its paralyzing action resembled 

 that of extracts of Cyanea tentacles, it appeared that Metridium extracts contained an 

 active material other than an Me^N-like component. 



At Bimini it had been found that tetraethylammonium chloride (EtiN) had an 

 action opposite that of Me4N and, likewise, that the actions of acetylcholine and its 

 triethyl analogue (EtjAch) differed one from the other. Large doses of Et4N could be 

 injected into H. nudus with little effect. For example, 5 crabs were injected with 

 0-05 ml of 10% EtiN. There were no spontaneous autotomies. In five minutes there 

 were some twitching movements of the legs and the crabs were hyperexcitable, but 

 twenty minutes after the injection they were normal in appearance and action. 



