Question

Notice the segments that occur in Lumbriculus. Can you tell a difference between a complete and posterior regenerated worm? Does this look like regeneration via epimorphosis (new cell proliferation at cut) or morpholaxis (rearranging existing tissue to compensate)?

                    

Answer 1

•The aquatic worm, Lumbriculus variegatus, replaces lost body parts after amputation by activating two distinct developmental processes: epimorphosis and morphallaxis.

•Epimorphosis involves stem cell differentiation and blastema formation during the compensatory replacement of lost body segments.

• Morphallaxis, the reorganization of original (intact) structures without the recruitment of cell proliferation .

•When worms regrow missing body parts, one of two general regeneration patterns seem to be followed.

1.One pattern is segment regeneration by compensatory growth. That is, the number of regenerated segments exactly equals the number removed. So, for example, if five head segments are amputated, then exactly five segments head segments regenerate in their place. Thus, with this pattern, all newly regenerated segments acquire precisely the same positional and numerical identity as the segments which were removed.

2.An alternative pattern is that the number of regenerated head segments is a constant. So, regardless of whether 5 or 25 head segments are amputated, only a fixed number of new head segments regenerates in their place. If this happens, then a developmental reorganization of the segments adjacent to the new head also occurs. That is, adjacent segments become transformed anatomically and physiologically to match their new positional identity along the body axes. This reorganization, which can occur without cell division, is called morphallaxis

•Head and tail regeneration in amputated fragments that have approximately the same number of segments but differ with respect to their original position within the longitudinal body axis.

•Segmental regeneration in Lumbriculus is asymmetric; that is, body fragments stereotypically regenerate only eight new head segments on anterior ends and tails of variable length on posterior ends

•The replacement of lost segments in Lumbriculus occurs as a process of epimorphosis, which involves the formation of a wound blastema that further differentiates into new head and tail body parts . As amputated fragments always regenerate a head of 7–8 segments in length, the original fragment segments undergo a morphallactic regeneration, which involves anatomical, physiological, and behavioral reorganization of those segments .

•Answer :- we can say that during blastula generation when the worm developed form both side segment [head and tail] it is called complete. Which is under the process of Epimorphosis.

•When the worm developed variable length tail posteriorly[under the control of neural Morphallaxis ] it is in