now begins to grow faster at two places than at intermediate points, as shown in Fig. 40, _H_. The new tail, although very short, assumes, as a result, the characteristic bilobed form. The point of special interest is that the new material that appears over the exposed edge does not first grow out at an equal rate at all points until it reaches the level of the original fork, and then continue to grow faster in two regions to form the lobes of the tail, but the two regions of most rapid growth are very soon established in the new tail. Subsequent growth in all parts of the new tail enlarges it to the full size. [Illustration: FIG. 3.--_A_, _B_. Short head-ends of _A. fœtida_ that did not regenerate at posterior surface. _C_, _D_, _E_. Longer anterior pieces, that made new segments at their posterior ends. _F._ After Hazen. A piece consisting of five (3 to 7) anterior segments grafted, in a reversed position, upon the anterior end of another worm. A heteromorphic head of about two segments regenerated at the free end, which is the posterior end of the piece.] In some cases of regeneration, in which the new part is at first smaller than the part removed, the new part represents at first only the distal portion of the body, and although the new part may grow to the full size, the whole of the part removed may never come back. This is illustrated in the regeneration of the anterior end of the earthworm; for example, in the red-banded earthworm, or brandling (_Allolobophora fœtida_).[7] If one segment of the anterior end is cut off, one segment is very quickly regenerated (Fig. 2, _B_); if two segments are cut off, two come back (Fig. 2, _C_); if three segments are cut off, as many are regenerated (Fig. 2, _D_); if four are cut off, generally four come back (Fig. 2, _E_); when five are cut off, four or five come back (Fig. 2, _F_); but if six or more are cut off, only four or five are regenerated (Fig. 2, _G_). It is found in this case that a limit is soon reached beyond which fewer segments are produced than have been removed. The new segments form the anterior end or head that enlarges to the characteristic size; but the missing segments behind the new head are never regenerated, and the worm remains shortened throughout the rest of its life. If the reproductive region has been removed with the anterior part, new reproductive organs are never formed and the worm remains incapable of reproducing itself. This same relation between the number of segments cut off from the anterior end and the number that is regenerated seems to hold good throughout the whole group of annelids, although the maximum number that comes back may be different in different species. Thus in lumbriculus six or seven or even eight new segments come back if more than that number have been removed.