ZO5] REGENERATION OF CRAYFISH APPENDAGES I 7 



that this also marks a constriction where a joint would have been 

 formed. The cleft at the distal end is a very good indication of 

 the separation of propodite and dactylopodite. The distortion 

 which the appendage naturally suffered from its close quarters 

 makes it very difficult to distinguish the different segments, yet 

 the usual differentiation of tissues has taken place, as can readily 

 be seen by reference to Fig. ii, PI. I. And at any rate. Figs. 

 9-1 1, PI. I, are sufficient to show that, although no regeneration 

 is apparent externally, this is no proof at all that regeneration 

 has not taken place. Fig. 12, PI. II, shows a part of the tissue 

 from the region a (Fig. 11) highly magnified. This tissue con- 

 sists of broad granular fibers with large nuclei. In Fig. 13, PI. 

 II, tissue frotn the region e (Fig. 11) is represented. Here the 

 fibres are more definitely formed, and between the two bands of 

 fibres, m and n, lies a space filled with coagulated plasma. 



Little more need be added in regard to regeneration of the 

 ambulatory appendages. The process is essentially the same in 

 them as in the chelipeds, except that very often the regenera- 

 ting appendage is longer in appearing than in the case of the 

 chelipeds. This, however, does not always hold true, for some- 

 times the papilla appears within three or four days after the 

 break occurs. 



2. TAIL-FINS. 



It was formerly supposed that the sixth pair of abdominal 

 appendages which, with the telson, make up the tail-fin, does not 

 regenerate when removed. Herrick ('95, p. 104) mentions that 

 lobsters are sometimes caught in which the tail-fin and even one 

 or two of the posterior abdominal segments are missing. None 

 of these lobsters ever show any signs of regeneration. Morgan 

 ('98, p. 294), however, finds that in the hermit crab the sixth 

 abdominal appendages do regenerate. 

 (2) 



