Regeneration of the CheUc of the Gnlf-ivced Crab. 



DISCUSSION. 



The relation between the molting period and the size or age of the crab. — 

 Observations on Crustacea show that in general the molting period in- 

 creases in length with age. In Portunus sayi this is true only to a very 

 limited degree in animals between the sizes of 3 and 15 mm. It is probable, 

 however, that very small individuals have a shorter molting period and very 

 large ones a longer one. It is interesting to note in this connection that 

 various observations have been made indicating an irregularity in the nmlt- 

 ing periods at different ages. Thus, in crayfish, Andrews finds that the 

 increase in length of the molting periods with age is not regular. 



The relation betzveen the length of the molting period and the amount of 

 regeneration taking place during the period. — The periodic casting of the 

 exoskeleton in Crustacea and its profound physiological effect upon the 

 whole organization of the animal introduces a factor which has important 

 bearings upon the rate of regeneration. The nature of this relation is im- 

 perfectly known, but recent work by Emmel ( 1906) and others has thrown 

 considerable light on the subject. It is evident that in dealing with Crus- 

 tacea the molting factor must be eliminated as nearly as possible. One 

 source of error was eliminated in the present experiments by making all 

 operations on the day after a molt, so that all might have the same relation 

 to the molt. The further question arose as to whether or not the length of 

 time between the operation and the molt has any relation to the amount of 

 regeneration. In other words, does regeneration go on at a uniform rate, 

 regardless of the length of the molting period? The results of the present 

 experiments show that, other things being equal, there is very little dift'er- 

 ence between the amount of regeneration in long periods and in shorter 

 ones. This statement needs only the qualification that between the longest 

 and the shortest periods there is an obvious difference between the amounts 

 in favor of the longest periods, but this is not sufficient to give these a rate 

 of regeneration even approximating to that of the shortest periods. This 

 result makes it necessary in dealing with the comparison of amounts of re- 

 generation to disregard length of time and to use the molting period as a 

 unit. At least this is necessary until the common relations of molting period, 

 size of animal, time of operation with reference to the molt, and amount of 

 regeneration have been more fully worked out than they are at present. 



The relation between the cephalo-thoracic length and the amount of re- 

 generation. — Some work has been done upon the effect of age of an indi- 

 vidual upon its power to regenerate. The general conclusion has been 

 reached that the power to regenerate is less highly developed in older than 

 in younger individuals, though notable exceptions to this rule have been 

 found. In most of this former work the statements made have been un- 



