Further observation on the early regenerates after fission in the planarian Dugesia japonica

In addition to possessing remarkable regeneration powers, many species of planatians reproduce asexually by fission. Since fission takes place at the post-pharyngeal region in most cases, we amputated this body portion of intact animals and compared their regeneration process with that of fission fragments. The fission fragments formed a well-defined blastema in the early regenerates, and the number of blastema-forming cells of the regenerates was larger than that of the amputated ones. When we compared the early regenerates from posterior fragments with those from anterior ones, it was clearly confirmed that posterior fragments invariably regenerated more rapidly. The present observations on the pre-fissioning planarians suggest that the rapid development of the early blastema is induced by fixed parenchyma cells at the preparatory parenchymal region for fissioning.