368 Charles Zeleny. 



rise of the response curve in many instances. May not the 

 acceleration of the regeneration rate with an increase in injury 

 to the animal be explained on a similar basis? 



6. In a series of experiments on the opercula of the Serpulid 

 worms it was shown that when the large functional operculum 

 is cut off near the middle of its stalk the small rudimentary oper- 

 culum of the opposite side develops into a functional operculum 

 while the remaining stalk of the old functional drops off at its 

 base and in place of it a new rudimentary operculum is developed. 

 The final result of the operation is therefore a reversal in position 

 of the opercula. When the rudimentary operculum is cut off a. 

 new rudimentary is regenerated in its place. When the whole 

 head region of the animal is cut off the two opercula which are 

 regenerated are equal in size and resemble the old functional one.^ 

 It seems therefore that when one of the regenerating buds gets a 

 start over the other it holds the latter back at the rudimentary 

 stage. On the other hand when both buds have an equal start 

 two opercula of equal size are developed. A retardation stimulus 

 must be assumed to be given out by the functional operculum 

 which holds the rudimentary operculum in check. When the 

 organ is removed the retardation stimulus is likewise removed 

 and the rudimentary operculum is enabled to develop into a 

 functional one. 



The same method of reasoning may be applied to the case of 

 the regenerating chelae of the crayfish. Each uninjured chela may 

 be assumed to exert a retarding influence upon the growth or 

 regeneration of all the others. When only one chela is removed 

 the number of uninjured limbs remaining is greater than when 

 the other chela and the last two pairs of^ walking legs are also 

 removed. The retardation influence in the former case is there- 

 fore greater than it is in the latter and correspondingly the rate 

 of regeneration in the former case is smaller than it is in the latter. 



The term "retardation influence or stimulus" is undoubtedly 

 a very vague one. It may perhaps be best considered as a nervous 



'The results obtained for the chelae of Alpheus are essentially similar except in the case with both 

 chelae removed where the regenerating chelae are not alike. The difference here is probably due to the 

 fact that the removal of both chelae at their breaking joints leaves a basal stump on each side and is 

 not a total removal as in the corresponding case of the Serpulid opercula. However, the resulting 

 chelae even here show an approach toward similarity. (See Przibram, '01, Arch. Entw. Mech., xii; 

 Wilson, '03, Biol. Bull., iv; Zeleny, '05, Journ. Exp. Zool., ii.) 



