Lizards with double tails have often been described,[63] and it now appears that all these cases are due to injuries to the normal tail. Tornier has succeeded, experimentally, in producing double and even triple tails. If the end of the tail is broken off, and the tail is then injured near the end, two tails may regenerate, one from the broken end and one from the region of injury (Fig. 43). Under natural conditions this might occur if the tail were partially bitten off and the end of the tail lost at the same time. A regenerated tail may produce another tail if it is wounded. A three-tailed lizard may be made by cutting off the tail and then making two injuries proximal to the broken end. Two of the new tails may be included in the same outer covering if they arise near together, as shown in Fig. 43, _B_. Lizards with two or three tails may be produced in another way. If the tail is cut off very obliquely, so that two or three vertebræ are injured, there arises from each wounded vertebra a cartilaginous tube that forms the axis of a new tail. Tornier thinks that the regeneration is the result of overnourishment of the region where the injury has been made, but this does not seem in itself a sufficient explanation. Tornier has also been able to produce, experimentally, double limbs in _Triton cristatus_ in the following way: The limb is cut off near the body, and, after the cut-end has formed new tissue, a thread is tied over the end in such a way that it is divided into two parts. As the new material begins to bulge outward it is separated into halves by the constricting thread, and each part produces a separate leg (Fig. 43, _D_). The soles of the two feet in the individual represented in Fig. 43, _D_, are turned toward each other. The femur is bifid at its outer end, and to each end the lower part of one leg is attached. The bones in this part are fused together at the knee, so that only the foot portions can be separately moved. [Illustration: FIG. 43.--After Tornier. _A._ _Lacerta agilis._ Produced by partly breaking off old tail. New tail arises at place of breaking. Old tail also remains. _B._ Three-tailed form--two tails being united in a common covering. Old tail had been cut off (it regenerated the lower branch from cut-end) and two proximal vertebræ that had been injured. _C._ Additional limb of _Triton cristatus_ produced by wounding femur. _D._ Double foot of _triton cristatus_ produced by tying thread over regenerating stump. _E._ Foot of _Triton cristatus_. Dotted lines indicating how foot was cut off. _F._ Regeneration of same. _G._ Another way of cutting off foot. _H._ Result of last operation.]