106 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



In the young the flagelluin of the second antenna may be completely restored 

 without a molt taking place; in the adult one molt at least appears to be necessary 

 for complete restoration. In the fifth stage already mentioned, the anteunary flagelluni 

 was restored in about fifteen days. The fiagellum appears first as a papilla or bud, 

 which becomes sickle-shaped and finally coiled (figs. 100, 179). 



Fig. 100 is from the molted shell of a lobster 18 mm. long (No. 34, table 34). It lost 

 its right antenuary fiagellum in molting, July 25, and molted again in two weeks' time. 

 The drawing shows the condition which the regenerating appendage had reached in 

 the interval between the molts. After the last molt it was completely restored. This 

 figure illustrates tbe stage which the appendage usually reaches before its complete 

 renewal with the next molt. The fiagellum then resembles a small, spirally coiled, 

 red-wax taper. In fig. 179 this appendage is being renewed from the first joint. 



The cuticle of the limbs in process of restoration must be elastic or capable of 

 considerable distension, although the limit of this distensibility is, in most cases, soon 

 reached. 



In the isopod Crustacea the antennae are regenerated in a somewhat different 

 manner. In the case of the large Ligea oceanica, illustrated in figs. 180, 181, plate 44, 

 the rent is repaired, and the new bud does not grow out from the stump, but coils 

 up within it. The cuticular wall of the stump serves as a sort of brood chamber for 

 the growing part, until it is set free at the next molt. 



Autotomy often occurs in the secoud to fifth pereiopods, but is much feebler than 

 in the large chelipeds. Two stages in the regeneration of these appendages are shown 

 in figs. 175, 178. The fourth pereiopod of a fourth larva, drawn from the molted skiu, 

 is illustrated in fig. 99, plate 33. 



Reaumur (161) was one of the first to attempt to give a philosojmical explanation 

 of regeneration in Crustacea. He says: 



We may suppose that these little limbs which we see grow out were each inclosed in a little egg, 

 and that when a limb was broken off the same juices which nourished this part were used to 

 develop and bring to the birth the little germ of a limb inclosed in this egg. Moreover, according to 

 this theory, we should have to suppose that there was no spot in a leg of the crayfish where there 

 was not an egg which incloses another limb or, what is more marvellous still, a part of a limb like 

 that near the point where the egg is situated at the end of the limb; in short, at any point in the leg 

 which you may name there must be one of these eggs, which contains another part of the limb. The 

 eggs which are at the origin of each claw, for example, would contain only a claw : but one egg 

 would not be sufficient, since if a new leg is cut off another comes. 



How many times this process could be repeated without exhausting the supply 

 of "eggs" he did not determine, but Spallanzaui, according to Weismann, ''observed 

 in the case of a young Triton, that the four limbs and tail when they were cut off 

 grew again six times in the space of three summer months." (The Germ-Plasm, p. 

 120.) Reaumur believed that each new limb must contain an infinite number of eggs, 

 and in conclusion says : 



It would seem that the reproduction of the legs of the crayfishes is a matter where we can scarcely 

 hope to see clearly ; besides its peculiar difficulties, it has all those which envelop the generation of 

 the foetus. 



It is over eighty years since these words were written, and the solution of the 

 problem of regeneration seems to some as far away as ever. The new limb is not 

 formed from a definite cell or cell-mass recognizable before the time of injury, but 

 from a budding growth very much as in the embryo. 



