Sensory reactions of Holothuria surinamensis. 245 



■dioxide, uric acid, or urea ^) had been added ; low concentrations of 

 tannic acid were also used. These experiments gave no definite 

 results, as aiitotoray was produced with some individuals and 

 not with others; and even in the first instances autotomy was 

 observed only after the lapse of such an interval (10 — 12 hours) that 

 seawater originally normal might have produced the same effect. 

 That some pathological state is induced by the stale water is 

 strongly indicated by the fact that animals kept over night in a 

 small volume of seawater were frequently observed to eviscerate 

 after being transferred to fresh seawater; and further, that after 

 the holothurians in an aquarium had begun to eviscerate, areation 

 of the water by splashing did not put a stop to the process. 



Chemical irritation of a different sort was found to initiate 

 autotomy in a majority of cases. It is almost impossible to an- 

 aesthetise Holothuria and keep it intact. Caibon dioxide was the 

 most successful anaesthetic employed ; the use of chloralhydrate^ 

 magnesium sulphate, chloretone, cocaine, or urethane did not give 

 good results. Immersion in fresh water led to partial evisceration 

 in four out of ten experiments. Dropping the animals into formalin 

 (5 per cent, or stronger) or into 70 per cent alcohol, invariably 

 produced more or less complete autotomy when some of the irri- 

 tating material had been drawn into the cloaca in the course of a 

 respiratory movement. 



The integrity of the nervous system is not essential for the 

 act of autotomy, though it is more sucessfully carried out by the 

 intact animal. The following experiment will illustrate this point: 



Exp. 85,2. 



2. July 21. 10 animals had 5 — 7 mm of the anterior end, includ- 

 ing the ring structures, removed by a rapid cut; 8 of these showed part 

 of the respiratory trees extruded through the cut immediately after the 

 operation ; 2 individuals expelled the gut through the new anterior end 

 within five minutes after the operation. No fourther autotomy observed 

 in this lot; kept until July 25th. 



The only conclusion which seems justified from these experi- 

 ments is that visceral autotomy is the result of a pathological con- 

 jars ; when cool, the holothurians were introduced and the jar quickly 

 resealed. The resistance to lack of oxygen shown by Holothuria is 

 paralleled by that of many other marine animale (MoOEE, 1913). 



1) Fosse (1913) has identified urea in echinoderms and their- 

 excretory products. 



