Differentiation capacities of the dorsal metathoracic (Haltere) disc ofDrosophila melanogaster : II. Regeneration and duplication.

Anterior fragments of mature haltere discs are shown to regenerate missing anlagen when allowed additional growth in adult hosts. It appears that a small part of the scabellum anlage, and perhaps even the metathoracic anlage alone, is capable of regenerating a complete haltere. Posterior fragments are capable of duplicating the anlagen present in them, often with perfect mirror-image symmetry. Symmetrical structure is already observed in the cultured disc fragments prior to differentiation in the final host. Beside polarized duplication, local multiplication of units or size increase of structures was observed.The present results are interpreted in terms of a monotonic gradient of positional value running through the dise in an anterior-posterior direction. Fragments containing higher parts of the gradient would be able to regenerate lower parts in the blastema during growth, whereas in the case of proliferating fragments containing lower gradient parts a zero boundary would be established at the tip of the blastema, leading to polarity reversal in the middle of the total tissue mass.