REGENERATION AND LIABILITY TO INJURY

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Abstract
The results, taken as a whole, show that the first three walking legs are most often lost. The last two thoracic legs were not absent in a single case examined, and the same statement holds for the last abdominal appendages. The second (♂) and third (♀) abdominal appendages were absent in one case each, but whether from individual variation or from loss during life is not known. Yet, since in one case small abdominal appendages were found, it may be that these appendages are sometimes lost. Shall we find, then, in the regeneration of these different appendages any correspondence between the power of regeneration and the liability to injury or loss of a part? In three cases the leg had not regenerated; in one of these the leg had been cut off very near to the body, and in the other two cases two legs of the same crab, presumably thrown off after injury, had not regenerated. Seven new legs were forming, and three others had the beginning of a bud. In three cases in which the tip of the leg had been cut off no new part formed. As these legs were in constant use, any new tissue would, perhaps, even if it formed, be worn off. From another series one of the last two thoracic legs or the first, second, or third abdominal appendage was cut off on June 12. On July 2 the crabs were killed and examined. Thirty-one individuals were present at the end of the experiment, and of these five were regenerating the fourth leg, and four showed as yet no signs of regenerating the lost leg; six were regenerating the fifth leg; three were regenerating the first abdominal appendage, but nine showed no signs of regeneration in this appendage; two were regenerating the second abdominal appendage (♂), and four were not regenerated (♂). The results show that the small fourth and fifth legs possess the power of regeneration. The abdominal appendages (first, second, and third) have also the power of regeneration, but the percentage of those in which the process takes place is smaller than in the case of the thoracic appendages. Whether this difference is due to the longer time necessary for these appendages to grow again or to some difference connected with the place at which they were cut off is not clear. Whether a molt is necessary for the reappearance of the abdominal appendages I do not know. It may be that they do more rarely regenerate, and this in turn may be connected in some way with the amount of food supply brought to the region from which they arise. At any rate, the positive result in those cases where regeneration took place shows that these appendages still possess the power of regeneration. In another experiment one of the last abdominal appendages, the right or the left, was cut off on June 14. On July 2 all, with one exception, were regenerating. Eight individuals had a new, or regenerating, left appendage, and the right smaller appendage was regenerating in three cases. In a single case the absent right appendage had not regenerated. In the second series of experiments, made on August 18 and brought to a close on September 15, the eyes, antennae, antennules, and maxillipeds were cut off; and I also repeated the experiment of removing one or more of the first three or four (♀) abdominal appendages. The experiment shows that the abdominal appendages have the power of regeneration, although they do not regenerate as readily as do the more anterior appendages, or as do the last abdominal appendages. The positive evidence showing that the anterior abdominal appendage regenerated in several cases is, I think, of much greater weight than the negative evidence that they did not do so as frequently as the other appendages during the short time of the experiment. In regard to the relative usefulness of the abdominal appendages little can be said. In the male they are small and weak, and one, the third, present in the female, is absent in the male. In the female the first three abdominal appendages carry the eggs. They are, therefore, essential for the existence of the race; yet there is no difference found between the power of regeneration of the three anterior egg-bearing appendages of the female and the two corresponding appendages of the male.

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