H. V. BRONDSTED 



Accordingly, several sets of experiments were carried out with the purpose of find- 

 ing out the rate of head-regeneration from various parts of the body. The experiments 

 were made by cutting the animal in pieces according to a certain pattern and noting 

 the time necessary for the pieces to regenerate heads. (Brondsted, 1946; A. and H. V. 

 Brondsted, 1952). In this way it was found that there existed a static time-graded 

 regeneration field, different for each planarian species so far investigated. Figure 3 

 shows the extent and intensity of the field in Bdellocephala. The field is static in the 

 unwounded animal, and of course only displays itself after a cut has been made. 



Figure 1 . Bdellocephala 

 punctata after decapitation. 

 The median part has been re- 

 moved; eyes are regenerated at 

 both 'arms'. (Brondsted, 1946.) 



Figure 2. Bdellocephala 

 punctata. A quadrangular 

 piece has been removed; a head 

 is regenerated at the anteriorly 

 directed wound surface at the 

 posterior side of the 'window'. 

 (Brondsted, 1946.) 



The significance of such a dynamic structure is apparent. When the rate of re- 

 generation varies in the way shown, every cut will expose a surface in which some 

 place has the highest regeneration rate ; this place is called the high-point. From here 

 regeneration of the head starts, but in doing so it must at the same time inhibit 

 neighbouring parts from exercising their ability to make heads themselves. Thus 

 the time-graded regeneration field, together with an inhibitory action exercised 

 from the high-point towards neighbouring parts, ensures that only one head is 

 formed from the anterior-facing surface of a wound, and so leads to harmonious 

 regeneration. In order to test this hypothesis some experiments were carried out, 

 of which a full account will be published elsewhere. These experiments were designed 

 to demonstrate the inhibitory influence which must pass from the high-point to the 



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