446 Charles R. Stockard 



VI RELATION OF THE DEGREE OF INJURY TO THE RATE OF 

 REGENERATION 



The relation of the degree of injury to the rate of regeneration 

 has lately received considerable attention. Zeleny ('03, '05, '07) 

 has held that for the arms of the brittle-star, Ophioglypha, the 

 limbs of the crayfish, Cambarus, and the oral arms of Cassiopea 

 the rate of regeneration of each appendage is faster when several 

 appendages are removed than when only one is cut away. Em- 

 mel ('06) has shown in the larval lobster that each limb regenerates 

 more slowly when many are removed and faster when fewer. On 

 the other hand Scott ('07) finds that the fins of the fish, Fundulus, 

 regenerate at rates entirely independent of the number of fins 

 removed. The results are, then, not in accord and the disagree- 

 ment suggests that if the degree of injury does exert any influence 

 on the rate of regeneration such an influence varies for difi^erent 

 species and may not be so pronounced as to be an easily determin- 

 able factor. 



I have shown ('08) that medusae injured to the same extent 

 regenerate new oral arms at rates diff"ering as widely as do the 

 average rates of medusas injured to diff'erent degrees. Attention 

 was also called to a considerable individual difference between 

 the rates at which the several arms on one individual regenerate. 

 Miss King ('98) also found in Asterias that "the rate of growth 

 of the new arms is ordinarily unequal when a disk regenerates two 

 or more at the same time. " 



The investigations on Crustacea are open to the criticism that 

 growth here is not continuous. A new bud begins to grow and 

 completes the amount of growth possible within the rigid chitinous 

 body-wall and then ceases to grow until a molt occurs. Zeleny 

 ('05) found that in the crayfish the time elapsing between molts 

 was longer in animals that had been injured to a lesser degree 

 than in those more injured. Notwithstanding this fact the specific 

 amount of regeneration from all individuals is the same at the 

 time of the first molt independent of the degree of injury, the size 

 of the animal or the time elapsing between the operation and the 

 molt. Each bud thus seems to grow as much as possible and then 



