Studies of Tissue Growth 435 



animal is hardy and very resistant, being kept with ease in aquaria 

 where the water is changed on alternate days. In fact Cassiopea 

 remains in better condition when the water is not changed too 

 often since excessive agitation is detrimental to their welfare. 

 They were kept in four-liter battery jars, one or two individuals 

 in each jar, and were not fed during the time of the experiment. 



The brittle-stars are also abundant at Tortugas being readily ob- 

 tained in hundreds on the coral reefs. Four species were selected 

 for experiment, two of which proved unfavorable on account of 

 a tendency to throw off their arms. 



It was impossible to keep the ophiurans in a healthy condition 

 in the battery jars which serve so well for Cassiopea. Equally 

 unsuccessful attempts were made to keep these species in large 

 aquaria tanks supplied with intermittently running water. Floating 

 ''live-cars" were finally resorted to and these proved highly suc- 

 cessful. The "live-cars" were about 2 m. long by i^ m. wide 

 and were divided by means of plank partitions into small compart- 

 ments about 30 cm. square, thus facilitating the separation of the 

 several groups used in the experiments. In each compartment 

 was placed a small coral rock beneath which the animals might 

 hide, so providing a practically natural environment. These 

 coral rocks contained in their cavities many small animals, crus- 

 taceans, worms and molluscs, which doubtless furnished food for 

 the brittle stars, since they all increased in size during the forty- 

 nine days spent in the "live-cars." The conditions of the reef 

 were further imitated by the movements of the waves which kept 

 the water in the cars constantly changing and fresh. 



Ill THE INFLUENCE OF ACTIVITY AND REST ON THE RATE OF 



REGENERATION 



The relation of activity and rest to the rate of regeneration was 

 considered in my first paper on regeneration in Cassiopea. The 

 question seemed to be one of some interest since several authors 

 had attributed importance to activity as a probable factor in deter- 

 mining certain qualities in regeneration. The pulsating disk of 

 Cassiopea is so exceptional an object for testing such a question 



