The best opportunity to examine the regenerative power in similar organs of the same animal is found in forms like the crustacea, myriapods, and insects, in which external appendages are repeated in each or many segments of the body. In decapod crustacea, including shrimps, lobsters, crayfish, crabs, hermit-crabs, etc., regeneration takes place in the walking legs of all the forms that have been examined, and this includes members of many genera and families. I have made an examination of the regeneration of the appendages (Fig. 37) of the hermit-crab. In this animal, which lives in an appropriated snail’s shell, only the anterior part of the body projects from the shell. The part that protrudes is covered by a hard cuticle, while the part of the body covered by the shell is quite soft. Three pairs of legs are protruded from the shell. The first pair with large claws [Illustration: FIG. 37.--Appendages of Hermit-crab (_Eupagurus longicarpus_). _A._ Third walking leg. _B._ Next to last thoracic leg. _B¹._ Last thoracic leg. _C_, _C¹_, _C²_. Three abdominal appendages of male. _D._ Telson and sixth segment with last pair of abdominal appendages. _E._ Regeneration of new leg from cut-end outside of “breaking-joint.” _F._ Leg regenerating from cut made inside of “breaking-joint.” _G._ Leg regenerating from cut made very near the body.] are used for procuring food, and as organs of offence and defence; the second and third pairs are used for walking. The following two pairs, that correspond to the last two pairs of walking legs of crabs and crayfishes, are small, and are used by the animal in bracing itself against the shell. The first three pairs of legs have an arrangement at the base, the “breaking-joint,” by means of which the leg is thrown off, if injured. The last two pairs of thoracic legs cannot be thrown off. The first three pairs of legs are often lost under natural conditions. In an examination of 188 individuals I found that 21 (or 11 per cent) had lost one or more legs. If one of the first three legs is injured, except in the outer segment, it is thrown off at the breaking-joint, and a new leg regenerates from the broken-off end of the stump that is left. The new leg does not become full size, and is of little use until the crab has moulted at least once. The leg breaks off so close to the body, and the part inside of the breaking-joint is so well protected by the bases of the other legs, that it is scarcely possible that the leg could be torn off inside of the breaking-joint, and, as a matter of observation, all crabs that are found regenerating their legs under natural conditions do so from the breaking-joint. If, however, by means of small scissors, the leg is cut off quite near the body, a new leg regenerates from the cut-end, even when the leg is cut off at its very base. The breaking-joint would thoroughly protect from injury the part of the leg that lies nearer to the body, and yet from this inner part a