Leg regeneration in the cockroach,Blattella germanica : I. Regeneration from a congruent tibial graft/host junction.

The interactions occuring between graft and host leg epidermis at a congruent junction (non-rotated, homopleural combination of components cut perpendicular to the proximal-distal axis) were studied at the tibia level in the cockroach,Blattella germanica. Grafts were made between dark (Bl) and light (br) cuticle colour mutants. 1) Precise boundaries could not usually be drawn between Bl and br tissue over areas of bare cuticle but spines, hairs and claws could be identified, providing a good indication of the graft or host origin of regenerated structures. 2) When the graft tarsus remained intact, segmented structures were not regenerated from the junction. Host distal tibia and graft proximal tibia interacted to produce a reversed orientation intercalary regenerate, usually composed mainly of host cells which had become more proximal than their level of origin. 3) When the graft tarsus was amputated (or broken off), nearly 50% of congruent junctions regenerated segmented distal structures, which were classified as "autonomous" or "lateral". Amputation of the graft tarsus acted, not through removal of any inhibition, but by hindering healing of the junction because of the apolysis of graft tibial epidermis. 4) Distal structures regenerated autonomously by host and graft components of the junction were either complete or partial (fused at a common level in the tarsus). 5) Lateral regenerates were of joint origin and usually distally incomplete. They were stable and, when amputated, were regenerated to approximately the same level, in the presence or absence of the graft tarsus. 6) It is concluded that autonomous regeneration occurred from junctions which had totally failed to heal, and that lateral regeneration occurred from an unhealed sector of a junction. Laterals were therefore regenerated from a bilaterally symmetrical, partial circumference. They are compared to other incomplete regenerates found in analogous situations. The relationship between transverse organization and distal incompleteness is obscure. 7) Segmented structures are thus regenerated only in situations where host and graft do not heal and interact (at least initially) over all or part of the circumference of the junction: interaction results in the formation of an unsegmented intercalary regenerate comprising the levels normally lying between host and graft on the proximal-distal axis.