Extent and properties of the regeneration field in the larval legs of cockroaches (Leucophaea maderae): III. Origin of the tissues and determination of symmetry properties in the regenerates

Previous papers dealing with the regeneration field of cockroach (Leucophaea maderae) legs have shown that two elements of the leg surroundings are indispensable for regeneration of a leg: the basal sclerites and the ‘leg-inducing membrane’ (LIM). The experiments of this paper partly clarify the way in which these two tissues interact; the origin of the regenerative tissues and the determination of polarity and symmetry in the regenerated legs were studied. By combination of sclerites and LIM of different species or segments it has been shown that each of the tissues makes up half of a leg regenerate - the sclerite tissues the anterior longitudinal half, the LIM the posterior longitudinal half. The trochantin was implanted in four different orientations (normal, turned 90° clockwise or anti-clockwise, turned 180°) into a normally orientated field of LIM. The anteriorposterior and medio-lateral axes of the regenerates had the same orientation as those of the sclerites. Therefore, the sclerites alone determine symmetry of the regenerate; the LIM has no influence in this respect. Neither of the two axes is fixed irreversibly in the cells of the LTM; the cells seem able to accept any polarity which is forced upon them by the sclerites. The symmetry properties are more strongly fixed in the cells of the sclerites, but an inversion of polarity (through 180°) is possible for both axes. Regeneration of a leg from the level of the trochantin seems to be initiated by or dependent on a small medial region of the trochantin. A tiny fragment of the medial wedge ofthe trochantin, when transplanted to a field of LIM, can form a complete leg regenerate; a lateral half of the trochantin never does. As long as this small medial part of the trochantin is prevented from making contact with LIM by a praecoxa fragment, no regeneration takes place at the anterior border of the trochantin, even when the greatest part of the border has contact with LTM. The regenerative capacities of the praecoxal sclerite are different at the anterior and posterior cut surfaces, irrespective of the level of the cut and the orientation of the sclerite. An anterior cut surface never forms a leg regenerate, but a posterior cut surface does.