Intercalary leg regeneration in the large milkweed bug Oncopeltus fasciatus.

Grafting operations were performed on the metathoracic legs of fourth instar Oncopeltus fasciatus within 24 hr after ecdysis. Different levels along the tibia were combined so that a lengthened tibia, approximately 1.5 times the normal length, or a shortened tibia, about half the normal length, were created. Intercalary regeneration occurred between the graft and stump in both combinations and the extra tissue was visible on the adult leg. The intercalary regenerate produced by the lengthened tibia showed reversed bristle polarity, while that produced in the shortened segment showed normal polarity. It is suggested that a regenerate with reversed polarity represents a mirror image duplication of the graft and might originate from the graft, whereas a regenerate with normal polarity may originate, as in normal regeneration, from the stump. It appears that each level in the appendage has the developmental capacity to produce only more distal structures. This conclusion is supported by the results of a grafting operation in which a portion of the tibia was grafted back on to the stump with its proximo-distal axis reversed. Regeneration of appropriate distal structures proceeded from the free proximal surface of the grafted tibia.