Compensatory Regulation. 



99 



From the point of view of the retarding influence exerted by 

 one organ upon another the data that have been brought out in 

 the present paper may be collected in the following concise form : 



J . Ophioglypha. Arms a, h, c, d, e. 



ai = Rate of regeneration of an arm when it alone is cut off. 

 ao = Rate of regeneration of an arm when two arms are cut off, etc. 

 ra, = Retardation as result of influence of remaining arms on ai, etc. 

 Then 



as = ^4 + ra4 = «3 +ra3 = 02 + ra., = fli + ra, 

 arms remaining = none, e, (^ and ^, <:,^andf, h,c,d2iX\Ae. 



In the above as > ^4 > as > 02 > 

 and O < ra4 < ran < rao < 

 2. Hydroides. Opercula, OpRorL and ORLorR- 



OpRorL = Functional operculum, right or left. 

 Orlofr = Rudimentary operculum, left or right. 



Taking for the sake of simplicity the opercula as Ofr and Orl we have: 



ai 

 ra,. 



Operation. 



(i) Bothofl^. 

 (thoracic cut) 



Result. 



Ofr + Ofi 



Explanation on " Retardation " Theory. 



(2) Functional off. = Orr + Ofl 



(3) Rudimentary off. = Ofr + Orl 



No retardation of one by the other. 

 Therefore both reach full develop- 

 ment. 



Reversal of opercula. Release of 

 normal retardation of old rudimen- 

 tary and the presence of a new 

 retardation influence upon the new 

 rudimentary. .'. a reversal. 



Full action of old retardation influence 

 upon the new bud and therefore no 

 change. 



3. Gelasimus. Chelae Cr, Cl. Asymmetry in c? only. 



In c? one chela is considerably larger than the other, but the condition is fixed 

 and cannot be reversed as can the opercula of Hydroides. 



In 9 the two chelae are equal. 



Cr + Cl, as compared with Cr alone orCL alone, shows an acceleration of the 

 time of moult and has each chela bud larger than the single bud of the latter. 



4. Alpheus. Chelae Cr, Cl. Asymmetry in both c? and 9 . 



The basal ganglia controlling the chelae are similar on the two sides (Brues). 

 (i.) Reversal takes place as in Hydroides. 



