9^ Charles Zeleny. 



the same time, as from the anterior cut surface of the thorax, 

 two functional opercula are formed. 



Similarly, in the Decapod Crustaceans the two chelae have a 

 profound influence upon each other. 



In Alpheus there are two chelae, one a larger "snapping" 

 chela and the other a smaller "cutting" chela. The snapping 

 chela seems to hold the cutting chela in check, for as soon as the 

 former is thrown off the cutting chela changes over to the snapping 

 chela by a qualitative and quantitative change combined. The 

 new organ regenerating in place of the old snapping chela comes 

 into a system no longer relatively like the old, so that the inter- 

 action of parts forces it into a difi^erent niche in the new order of 

 things. The reversal, here as in the Serpulids, is easily under- 

 stood in the way mentioned, if we consider the systems as asym- 

 metrical interacting systems such that the removal of one part can 

 lead only to the development of a certain definite structure. The 

 removal of the organ (functional operculum or snapping chela) 

 brings about an instability in the system which because of the 

 reactions between the parts tends to assume the condition of a 

 new stable system. This new system reacts now in a different 

 way on the regenerating organ, causing it to develop into a 

 different structure. The readjustment in the old material and 

 in the regenerating material is further complicated by the fact 

 that both processes go on at the same time, the final outcome 

 being the resultant of both. 



In Alpheus as also in Gelasimus w€ have an interesting relation 

 between the two chelae, in that when both are removed the rate 

 of regeneration is greater in each than when one alone is removed. 

 Evidently this comes under the Ophioglypha relation that the 

 presence of an unremoved organ retards the rate of regeneration 

 of a removed one. Likewise if we consider the cutting chela of 

 Alpheus as a stage in the development of the snapping chela 

 (Wilson, '03) and the rudimentary operculum as a stage in the 

 development of the functional, we can say that the presence of 

 the larger organ retards the differentiation of the smaller one. 

 This comes into relation with the series of experiments on the 

 rate of differentiation of the regenerating opercula in Apomatus, 

 in which it was found that the absence of the posterior region of 

 the body back of the second or fourth thoracic segment accelerates 

 the rate of differentiation of the regenerating opercula. 



