2 J. WILLIAM BUCHANAN 



lobes are approximated to the median line and the eye is single 

 and median; anophthalmic (F), in which there is more or less 

 anterior regeneration, but no eye; headless (G), in which there 

 is no appreciable anterior regeneration, merely a healed wound. 

 These external characteristics are indices of the degree of devel- 

 opment of the cephalic ganglia (Child and McKie, '11). The 

 term 'head frequency' has been applied to the frequency with 

 which heads of these types appear in a given number of pieces. 

 An examination by Child of the nature of regeneration and 

 head frequency in pieces from different regions of the body of 

 several species of Planaria, particularly Planaria dorotocephala, 

 has led him to the conclusion that the conditions controlling 



A 



r^ 



A 



B 



D 



E 



Fig. 1 A, Normal form. B, C, D, three types of teratophthalmic forms. E, 

 teratomorphic form. F, anophthalmic form. G, acephalic, or headless form. 



the degree of regeneration are primarily physiological and 

 quantitative, not morphological and specific. He supports this 

 conclusion with data showing that controlled changes in the 

 physiological conditions of the animals by feeding, starvation, 

 temperature, mechanical stimulation, and the action of certain 

 chemicals bring about controlled changes in head frequency, 

 either increases or decreases, in pieces from any region of 

 the body. 



Furthermore, it is evident from the data that changes in the 

 physiological conditions in the animals which bring about changes 

 in head frequency are quantitative changes, and not specific. 

 For example, the rate of oxidative reactions, whether deter- 

 mined by differences in age, or nutrition, or by chemical agents 



