Normal Heteromorphism in Earthworms

Abstract

Normally organized heteromorphic regenerates mentioned in the literature are of four species. Heteromorphic heads and tails from Perionyx sansibaricus and Ocnerodrilus occidentalis, as well as a heteromorphic tail from Gordiodrilus peguanus, are recorded. A heteromorphic head was developing at 47/48 on a specimen of the common lumbricid Allolobophora tuberculata. The pre-intestinal region is able, regardless of direction, to regenerate only a head or some portion of one. The intestinal region can regenerate heads as well as tails and at certain levels one or the other as determined by unknown factors of internal environment. Anterior heteromorphism, a tail regenerated instead of a head, was discovered by Bonnet in oligochaetes (possibly including some earthworms) as long ago as 1745. Posterior heteromorphism, a head regenerated instead of a tail, was not recognized in earthworms until around 1925. Heteropolar growths may be monstrous in various ways, or a regenerate may be heteromorphic only in part and then also in different ways. Normal regenerates, i.e., solely cephalic or caudal, with normal metamerism, and lacking outgrowths or other aberrations, have been recorded in the literature from four species of earthworms, as follows: Criodrilus lacuum, European, with segments to 450. One heteromorphic head (Janda, 1926) of 16 segments at intersegmental furrow 22/23, a head of 20 and another of 23 segments at unknown levels. Heteromorphic tails rarely were obtained and then only from adults. No data were published as to kind of operation, level of regeneration or number of segments in regenerates. These heteropolar tails may have been produced by fragments with two cut surfaces as in Eisenia foetida or by short terminal portions as in species of Perionyx. Eisenia foetida, of European origin but widely distributed in America, with 100-125 segments. Heteromorphic tails (Gates, 1949) regenerated at levels 20/21-54/55, number of segments increasing to a maximum of 25 at 40/41 and then decreasing. Heteromorphic tails (Gates, 1950b) also were regenerated by fragments of various sizes cut out from a middle portion of the body. Regeneration of heteromorphic heads (Gates, 1950a) is probable, in favorable conditions, at levels 16/17-34/35. Perionyx excavatus, of Himalayan origin but now widely distributed in the tropics, with 100-200 segments. Heteromorphic head regeneration (Gates, 1927, 1941, 1943) possible at 12/13-27/28 and has been induced merely by a simultaneously made second transection at subsequent levels back to 68/69. Heteromorphic tails regen1 From a manuscript written during tenuire of a John Simon Guggenheim fellowship.