Rate of Regeneration in Cassiopea xaniachana. 65 



and the medusa the rate of regeneration does vary under various conditions 

 of injury, but depends upon the body-level at which the cut is made. 



The Crustacea seem rather unsatisfactory forms for the study of such 

 [jroblems as the rate of regeneration. They must molt before the regenerating 

 portion can be observed and the time between molts is often greater than 

 the time which would be e.xpected as necessary for the given amount of 

 regeneration to take place. There is likely a period of cessation of regen- 

 erative growth preceding each molt. Animals which have a continuous 

 growth of regenerating tissue seem much better adapted to these studies. 



The experiments here recorded were conducted in the Laboratory of 

 Marine Biology of the Carnegie Institution of Washington, at Dry Tortugas, 

 Florida, during the summer of 1907. I wish to express my thanks to the 

 Director of the Laboratory, Dr. Alfred G. Mayer, for many kindnesses 

 e.xtended me while there. 



MATERIAL. 



The rhizostomous scyphomedusa Cassiopea xaniachana is very hardy. 

 It attains a large size, 15 or 20 cm. in diameter, and is particularly suited 

 to regeneration studies, as several e.xperiments or cuts may be performed 

 on one and the same individual where the conditions are as near similar as 

 would be possible to obtain. I-'urther, since all portions of the disk seem 

 capable of regeneration one may thus work on the animal's body as well as 

 on its tentacle-like appendages. Of exceptional importance is the fact that 

 the circular disk will admit of variously patterned cuts which are impossible 

 on animals with a differently shaped body. Finally, the disk pulsates rhyth- 

 mically in a manner subject to the control of the experimenter, thus enabling 

 him to test the influence of motion, or activity, on the regenerating tissue in 

 a way not offered by any other animal yet experimented upon. 



These medusae are easily kept for long periods of time in small aquaria 

 by merely changing the water every two or three days. They live for some 

 time without taking food. One may collect them in abundance from the 

 moat which surrounds the old Fort Jefferson at the Tortugas Islands. The 

 water in this moat is about 4 to 6 feet deep, being rather stagnant at times. 

 Here Cassiopea seems to thrive, and large numbers of them are to be seen 

 lying upon the bottom with their mouth-arms turned upwards, resembling 

 bunches of dark-colored moss. 



RATE OF REGENERATION FROM THE PERIPHERY OF THE DISKS WHEN 

 CUT AT VARIOUS DISTANCES FROM THE MARGIN. 



It is well to consider first the less complex cases in which an attempt was 

 made to determine the difference in regeneration rates from cut surfaces on 

 the disk of Cassiopea at various distances from the margin. Medium-sized 

 medusae were selected for the e.xperiments, and the cut consisted in each 

 case of the removal of a peripheral strip from the entire disk. Such an 



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