Intercalary regeneration and level interactions in the fresh-water planarianDugesia lugubris

Summary The aim of the present experiments was the analysis of possible dorso-ventral regulation in planarians. The experiments employ half-thickness pieces obtained by a horizontal cut between the ventral and dorsal faces. When the dorsal face of an anterior part was superposed onto the ventral face of a posterior part (or vice versa) with its antero-posterior polarity reversed, both faces maintained their orgginal organization. When half-thickness pieces of the same face (dorsal or ventral) were fused by their transverse cut surfaces and cultured in vitro, intercalary regeneration ensued as it does in full-thickness pieces combined in the same manner. When a half-thickness piece was grafted to a distant site on the same face, the ensuing remodelling of tissues proceeded in the same manner as in similar experiments carried out earlier with full-thickness grafts. When full-thickness pieces representing different antero-posterior levels were joined so that the dorsal face of one fused with the ventral face of the other, intercalary regenerates were formed as if the pieces had been joined by their homologous faces-unless and terminal blastema appeared early on the suture. These experiments show that (1) there is no dorso-ventral self-regulating system: (2) the antero-posterior system resides in the periphery of the worm.