REGENERATION IN AN EARTHWORM, EISENIA FOETIDA (SAVIGNY) 1826. I. ANTERIOR REGENERATION

¹ Colby College, Waterville, Maine

Posterior substrates of E. foetida, cut exactly at intersegmental furrows, regenerated homomorphic heads at levels 1/2-23/24, with equimery at 1/2-8/9 and hypermery (+ 1) at 4/5 and 8/9. Heteromorphic tails regenerated at 20/21 and from 23/24 to 54/55. Behind 54/55, regeneration of heteromorphic tails was obtained only from tail regenerates and substrates conditioned by a previous regeneration. Gradient of segment number in heteromorphic tails appears to be of an inverted V-shape.

Starvation for 70 + days did not inhibit regeneration at 5/6 and 6/7 but all regenerates were hypomeric.

Hypermery and hypomery provide an adequate explanation of the origin of symmetrical homoeosis.

Regenerative capacity in a region from 20/21 to 23/24 is characterized as bipotential since an anterior regenerate, in that region, may be a homomorphic head or a heteromorphic tail.

Review of previous work on E. foetida provides indications that the region of bipotential regenerative capacity is even more extensive, with anterior limit of heteromorphosis possibly at or even in front of 15/16 and posterior limit of homomorphosis in region of 35/36.

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