The time-graded regeneration field in planarians 



of vitamins on differentiation, with special reference to the connexion between RNA, 

 amino-acid metabolism, and protein synthesis. There is much evidence, summarized 

 by Needham (1952), that in nerve cells morphogenesis is linked with RNA content 

 and protein synthesis. It might be suggested that gene activity directs protein syn- 

 thesis when this has reached certain levels, different for the different cell clusters in 

 the time-graded blastema. 



In conclusion, I stress the need for biochemical studies of the kinetics and time 

 relations of enzymatic processes concerned in morphogenesis, and of morphogenetic 

 studies of the time relations of the differentiation of totipotent cells from different 

 parts of the embryo, such as we are trying to make on different parts of the time- 

 graded morphogenetic field. 



SUMMARY 



Regeneration experiments with planarians have revealed the existence of a time- 

 graded regeneration field. It has been shown that in the regeneration blastema there 

 exists a median high-point, or rather a right and left one close to the mid-line, which 

 starts earliest in making head structures. It has been shown that inhibiting forces 

 emanating from the high-point prevent lateral parts of the blastema from differentiat- 

 ing into ganglia and eyes, thereby securing a harmonious regeneration. 



It has been made probable that the problem of bilaterality may be understood on 

 the basis of the time-graded field. It is suggested that polarity is in some way con- 

 nected with inhibition and the time-graded field. 



It is suggested that inhibition is a chemical mechanism of a serological nature 

 producing inability in neighbouring cells to reach the same cytoplasmic reaction 

 level as that of the cell from which the inhibition emanates. 



It is suggested that the time course of inhibition is correlated with the temporal 

 succession of gene-activity. 



It is suggested that RNA plays a major role in the setting up of the time-graded 

 regeneration field and in doing so is the basis of the time-dependent processes in the 

 blastema. 



Some suggestions are made for experimental procedures to test the working hypo- 

 thesis here set forth. 



REFERENCES 



Barth, L. (1941). Neural differentiation without organizer. J. exp. %ool. 87, 371-382. 

 Bonner, J. T. (1952). The pattern of differentiation in amoeboid slime molds. Amer. 



Nat. 86, 79-89. 

 Brien, P. (1937). La reorganisation de l'eponge apres dissociation, filtration et 



phenomenes d'involution chez Ephydatia fluviatilis. Arch. Biol., Paris 48, 185-268. 

 Brondsted, A and Brondsted, H. V. (1952). The time-graded regeneration field 



in Planaria (Dugesia) lugubris. Vidensk. Medd. dansk. ncturh. Foren. Kbh. 114, 443-47. 

 Brondsted, A. and Brondsted, H. V. (1953). The acceleration of regeneration in 



starved planarians by ribonucleic acid. J. Embryol. exp. Morph. 1, 49-54. 

 Brondsted, H. V. (1936). Entwicklungsphysiologische Studien uber Spongilla 



lacustris (L). Acta zool., Stockh. 17, 1-98. 



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