3O8 CHARLES ALBERT SHULL. 



ning." As a matter of fact there is noway to tell how soon after 

 March 28 the regeneration did begin, if indeed it had not already 

 begun at that time. 



To explain the slight regenerative power which he found in the 

 abdominal appendages of Enpagurns, Morgan suggested that the 

 food supply of these organs might be considerably less than that 

 of the thoracic legs. It seems to me quite unnecessary to make 

 this assumption, especially since I have shown that there is a rapid 

 and complete regeneration of the swimmerets in young specimens 

 of C, (Bartonius) bartoni. In this connection Emmel, '04, ob- 

 served that swimmerets in the lobster will regenerate more rapidly 

 than the pereiopods if the latter are cut " only a relatively short 

 distance below the breaking plane." And he questions whether 

 the supply of food material can explain the comparative difference 

 in the regeneration of pereiopods and swimmerets. Moreover, 

 if the limited food supply is responsible for lack of regenerative 

 power how must we regard the regeneration of two supernumer- 

 ary appendages in the abnormal swimmeret figured ? It seems 

 to me that some other explanation must be offered for the differ- 

 ence in regenerative power. 



It has been a common experience with those who experiment 

 with regenerative tissues, that the regeneration is always more 

 rapid and complete in young individuals than in old ones. This 

 fact is due probably to the greater plasticity, the more active 

 and mobile condition of young tissues. They are more nearly 

 embryonic in character, differentiation is not so complete, nor so 

 fixed as in the older tissues. Emmel's ('08) recent work on the 

 reversal of asymmetry in the lobster lends emphasis to this state- 

 ment. He says : " In the first four stages of the lobster's develop- 

 ment, a crusher may be produced on either the right or the left 

 side of the body by the autotomous amputation of the chela on 

 the opposite side the regenerated chela becoming a nipper. 

 During the fifth stage, although the chelae are still symmetrical, 

 the possibility for such experimental control disappears." 



Since differentiation is known to proceed at different rates in 

 different parts of the body, we may suppose that one part re- 

 tains its primitive condition longer than another. If any portion 

 of the adult regenerates less rapidly than another portion, may 



