8 SERGIUS MORGULIS 



star Ophicoma pumila I ('09a) found only occasionally a slight 

 increase in the regenerative rate when four or all five arms were 

 removed; finally, Stockard ('09a) concluded from his studies of 

 the medusa Cassiopea and two Ophiurans, that no definite influ- 

 ence is produced in either direction by varying the extent of injury, 

 the rate of regeneration being increased in some species, but either 

 remaining unaffected or even being decreased in others. 



In his latest paper concerning the relation between degree of 

 injury and rate of regeneration, Zeleny ('09b, p. 555) modified 

 somewhat his original opinion, declaring that " within moderate 

 degrees of injury a part regenerates more rapidly rather than less 

 rapidly when it has regenerating company than when it regen- 

 erates by itself." 



I have performed several experiments on Podarke obscura^ with 

 different degrees of injury in the hope of finding a means of recon- 

 ciling the opposed views, but the results of the experiments have 

 not justified my expectation. In speaking of "degree of injury," 

 it may perhaps be well to state — since the phrase has been some- 

 what misunderstood — that I am using it in exactly the same 

 sense as Zeleny did, to indicate the number of operations per- 

 formed upon an animal; and in my experiments worms regen- 

 erating tails were decapitated and compared with regenerating 

 worms having their heads intact. Complications arising froiii the 

 discontinuity of the growth processes, which are a source of serious 

 error in experiments upon Crustacea, are entirely absent in the 

 case of worms ; furthermore, it is a comparatively easy matter to 

 control the size of the worms used in the experiments, as well as 

 the level of the cut, and by keeping in the same dish both kinds 

 of regenerating worms — decapitated ones and those with heads 

 intact — the greatest possible smilarity of external conditions is 

 secured. So far as differences of sex are concerned, they have no 

 importance in determining the regenerative rate, as will be shown 

 later. 



1 These experiments were performed in the Laboratory of the United States 

 Bureau of Fisheries, Woods Hole, Mass., where I occupied a table during the sum- 

 mer of 1909. Contributions I and II are referred to in the Bibliography under 

 Morguiis 1909b and 1909c. 



