Rate of Regeneration in Cassiopca xainachana. 99 



permit, just as the crustacean's body increases in size until its inelastic case 

 will allow it to become no larger, and must then remain quiescent until the 

 molting time arrives, which may be weeks or even months distant. There 

 is also a great individual difference between the crustacean's appendages, 

 which renders difficult a comparison of the regeneration rates from the 

 different limb-stumps of the same specimen. CaSsiopca is free from such 

 objections, but it shows so much variation in the specific rates of regenera- 

 tion from different individuals that it would be difficult as well as misleading 

 to claim from the data, now at hand, that any relationship existed between 

 the degree of injury an individual had sustained and its specific rate of 

 regeneration. 



VII. Cassiopea seems to be resistant to slight changes in osmotic pres- 

 sure, as is indicated by its condition in concentrated and diluted sea-water. 



(o) Regeneration from the disk of Cassiopea was slightly retarded in 

 sea-water to which NaCl had been added. This retardation may possibly 

 be due to the direct action of the Na ion, although considering the weakened 

 condition of the medusae in such solutions they might be expected to regen- 

 erate slower than the normal. 



(b) Strong solutions of KCl also retard the rate of regeneration, but 

 weaker solutions seem to accelerate the process. 



(c) Solutions of CaClj in sea-water have a tendency to cause muscular 

 tetanus, the oral surface of the disk often tearing as a result of the violently 

 contracted condition. The rate of regeneration in all CaCL solutions was 

 very slow, in some scarcely any regeneration taking place for a number of days. 



(d) Magnesium chlorid in sea-water solutions exerts a rather indiffer- 

 ent influence over the rate of regeneration. 



The chemical experiments show no marked indication of a difference 

 in the specific action of the several ions upon the rate of regeneration. 

 Even though such a specific influence of these ions does exist, it would be 

 difficult to discover, owing to the complex nature of the processes regulat- 

 ing growth and regeneration. There is evident need of extensive and 

 careful study along these lines. 



