So many different phenomena are included at the present time under the term “regeneration,” that it is necessary, in order to get a general idea of the subject, to pass in review some typical examples of the process. The regeneration of different parts of the salamander shows some characteristic methods of renewal of lost parts. If the foot is cut off a new foot is regenerated; if more than the foot is cut off, as much is renewed as was lost. For instance, if the cut is made through the fore leg, as much of the fore leg as was removed, and also the foot, are regenerated; if the cut is made through the upper part of the leg, the rest of that part of the leg and the fore leg and the foot are regenerated. The new part is at first smaller than the part removed, although it may contain all the elements characteristic of the leg. It gradually increases in size until it has grown to the same size as the leg on the other side of the body, and then its growth comes to an end. Other parts of the body of the salamander also have the power of regeneration. If a part of the tail is cut off, as much is renewed as has been removed; if a part of the lower or upper jaw is cut off, the missing part is regenerated; if a part of the eye is removed, a new eye is formed from the part that remains; but if the whole eye is extirpated, or the whole limb, together with the shoulder girdle, is removed, neither structure is regenerated. In other vertebrates the power of regeneration is more limited. A lizard can regenerate its tail, but not its limbs. A dog can regenerate neither its limbs nor its tail. It has been stated that the new limb of the salamander is at first smaller than the one removed, but it may contain all the elements of the original limb. We find this same phenomenon in other forms, and since it is a point of some theoretical interest, a few other examples may be given. If the tail of a fish that has a bilobed form is cut off near the base, as indicated in Fig. 40, _G_, there appears over the exposed edge a narrow band of new material. The new part [Illustration: FIG. 2.--_A. Allolobophora fœtida._ Normal worm. _B-F._ Anterior ends of worms, which, after the removal of one, two, three, four, and five segments, have regenerated the same number. _G._ Anterior third cut off. Only five head-segments regenerated. _H._ Worm cut in two in middle. A head-end of five segments regenerated. _I._ Worm cut in two posterior to middle. A heteromorphic tail regenerated at anterior end.]