Table l. — R-values (mean ± standard error) of first walking legs of crabs after 

 multiple autotomy and treatment with Pb, Hg, and Cd at 0.1 mg/liter. 



(range 14-16 mm). At this concentration, cad- 

 mium retarded regeneration to an even greater 

 extent. This concentration of mercury was usually 

 toxic, and the data obtained were from four crabs 

 which survived the duration of the experiment. 

 Regeneration did not take place in these crabs 

 (Table 2). The cadmium, however, was not toxic, 

 and all crabs survived, the majority (60%) com- 

 pleting ecdysis by 28 days. There was no mortality 

 in lead, cadmium, or clean water in any of the 

 experiments. The majority of controls molted by 

 24 days. A second group of crabs (carapace width 

 13 mm, range 12-14 mm) was exposed to cadmium 

 and mercury at 1.0 mg/liter. Lead was not used in 

 this experiment. Because of the high mortality in 

 mercury in the previous experiment, 20 crabs 

 were exposed to mercury. By the 17th day, the 

 number surviving in mercury was reduced to 

 eight, the same percentage as survived the previ- 

 ous experiment. The amount of growth in these 

 crabs, though slight, was nevertheless much great- 



er than in the previous experiment. Likewise, the 

 retardation in cadmium was not as striking as in 

 the earlier experiment (Table 2). The majority of 

 controls molted by 21 days, whereas the majority 

 in cadmium molted by 28 days. After 2V2 wk, the 

 eight crabs remaining in mercury were trans- 

 ferred to clean water, which was then changed 

 daily, but they did not show evidence of recovery 

 within 4 wk after return to clean water, during 

 which time no significant growth occurred. 



Residue analysis revealed that the crabs ex- 

 posed for 2 wk to 0.1 mg/liter of mercury had ab- 

 sorbed 0.026 ± 0.001 ppm; those exposed to 0.1 

 mg/liter of cadmium had absorbed 0.50 ± 0.10 

 ppm; and those exposed to 0.1 mg/liter of lead had 

 absorbed 2.04 ± 0.55 ppm. 



Discussion 



Retardation of regeneration was a specific effect 

 of cadmium at both 0.1 and 1.0 mg/liter. At 0.1 



465 



