172 REGENERATION 



It is doubtful, however, whether in doing so he did not confuse 

 cause and effect. In other words, the morphogenetic dominance 

 of the apical region might be the primary phenomenon, and the 

 difference in physiological activity of the tissues its con- 

 sequence. So far it has not been possible to decide which of 

 the two hypotheses is correct. 



On the basis of experiments on regeneration in hydroid 

 polyps, Spiegelman (1945) has developed a theory which re- 

 duces the dominance of a cell group over its neighbours to 

 "physiological competition" between the cells by the absorption 

 of food substances and the secretion of noxious waste products. 

 It is possible that several phenomena in this field can be 

 explained in this way. However, in an investigation on the 

 mutual influences of rostral and caudal regenerate in transverse 

 sections of Euplanaria luguhriSj Raven and Mighorst (1948) 

 showed that in this case the facts are not what one 

 would expect on the basis of the theory of "physiological 

 competition". 



All examples discussed so far referred to so-called "total 

 regeneration", provoked by transection of the whole body. 

 However, the study of the regeneration phenomena which occur 

 after the removal of subordinate parts of the body has further 

 contributed to our insight into the mode of action of or- 

 ganisation fields. Interesting results were obtained in particular 

 in experiments on the regeneration of limbs and tail in 

 amphibians. 



If a limb or the tail of a larval or adult newt is cut off, a 

 regeneration bud, consisting of more or less indifferent cells, is 

 formed in the wound area. The origin of this material and the 

 processes resulting in the formation of the regeneration blastema 

 have in recent years been the subject of many investigations. It 

 has been found that, immxediately after the amputation of a limb, 

 a marked de-differentiation takes place in the tissues of the 

 stump near the wound area. A partial disintegration of skeleton 

 and musculature takes place, and this process supplies great 

 numbers of free cells of a more or less indifferent appearance. 

 In the course of the next few days, a regeneration blastema 

 forms in the cut. 



