[Developmental (amputation, transplantation), physiological (respiration) and histological investigations in two planarians related by polyploidy,Dendrocoelum Lacteum Müller andDendrocoelum infernale Steinmann].

1. In the present paper the planariansDendrocoelum lacteum and a related, polyploid speciesDendrocoelum infernale are compared using developmental, physiological, and histophysiological criteria. Regeneration of the suction groove, an organ located at the anterior end of the animal, was investigated. Also, respiration rates were determined, and the neoblasts stained using an RNA stain. Finally, I succeeded in obtaining heteroplastic chimeras. 2. The results of the regeneration experiments showed that the level of amputation determines whether and how fast the suction groove is regenerated. After amputation in the anterior half of the animal, the groove is regenerated the faster, the closer the level of amputation is with respect to the anterior end. This holds for both species. On an absolute level, the two species differ markedly from one another in their ability for regeneration:D. lacteum regenerates approximately 2.2 times faster than doesD. infernale.After amputations in the posterior half of the body, the groove cannot be regenerated anymore, as shown usingD. lacteum; no conclusions on these questions can as yet be drawn forD. infernale. In heteroplastic chimeras either species shows regeneration, althoughD. infernale is not stimulated, in heteroparabiosis, to regenerate the suction groove as frequently asD. lacteum. 3. Physiological and histophysiological studies revealed additional differences between these two species.D. lacteum consumes 1.75 times more oxygen than doesD. infernale. Neoblasts of the two species become stained differently by methylgreen pyronin-Y: the cytoplasm ofD. infernale neoblasts stains less strongly than that ofD. lacteum neoblasts. 4. Thirteen heteroplastic chimeras were analysed histologically. Because of the differences in nuclear size of the two species it is possible to determine the border betweenD. lacteum andD. infernale histologically. Except for local discontinuities in the epidermis, the interspecific contact of tissues shows no gaps. The heteroplastic parts grow together tissuespecifically: only homologous tissues of the two species become joined. Pyknotic nuclei or nekrotic tissue was not observed. There seems to be no incompatibility reaction between tissues of the two species, as indicated by the fact that heteroplastic tissue combinations lead to the formation of chimeras as frequently as do homoplastic combinations. However, heteroplastic chimeras by and large disintegrate somewhat sooner than homoplastic ones. 5. In 4 of 13 heteroplastic chimerasD. infernale-cells immigrated into tissues ofD. lacteum. This immigration involves 4 epidermis cells that are integrated close to the border betweenD. lacteum andD. infernale in the foreign epidermis. On the other hand in 2 heteroplastic chimeras, whoseD. lacteum part had been irradiated with a lethal dose of 8000 R prior to transplantation, noD. infernale-cell immigrated into the epidermis ofD. lacteum. As an unexplained consequence of heteroparabiosis, the heteroplastic parts of otherwise harmonious chimeras do not cooperate in locomotion. Equally unexplained is the observation of unexpected eye formation in certain heteroplastic chimeras. 6. The effects of heteroparabiosis and possible correlations between polyploidy, physiology, and evolution are discussed.