152 C. M. CHILD 



for example, may either decrease or increase the regulatory capac- 

 ity of pieces according to the region of the body concerned and the 

 method in which it is used. These opposite effects of the same 

 reagent used in the same concentration are due to the fact that 

 the process of head-formation in any given piece is the resultant 

 of two opposed factors and the cyanide or other depressing agent 

 may alter the relation between these two factors in either direction. 

 5. The axial gradient is not continuous and uniform from one 

 zooid to another, but each zooid possesses an axial gradient of its 

 own. The regulation of pieces in dilute KCN or other depressing 

 agents shows that the anterior region of the second zooid is in a 

 different dynamic condition from the posterior end of the first. 

 In general the same is true for any two zooids, but in the poste- 

 rior zooids which are only slightly developed, the differences be- 

 tween the posterior end of one and the anterior end of another are 

 often slight. 



BIBLIOGRAPHY 



Child, C. M. 1906 The relation between regulation and fission in Planaria. 

 Biol. Bull., vol. 11, no. 3. 



1909 The regulatory change of shape in Planaria dorotocephala. Biol. 

 Bull., vol. 16, no. 6. 



1911 a Die physiologische Isolation von Teilen des Organismus. 

 Vortr. und Aufs. ii. Entwickelungsmech., H. 11. 



1911 b A study of senescence and rejuvenescence, based on experi- 

 ments with Planarians. Arch. f. Entwickelungsmech., Bd. 31, H. 4. 

 1911 c Studies on the dynamics of morphogenesis and inheritance in 

 experimental reproduction. I. The axial gradient in Planaria doro- 

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 no. 3. 



1911 d Experimental control of morphogenesis in the regulation of 

 Planaria. Biol. Bull., vol. 20, no. 6. 



1911 e Studies on the dynamics of morphogenesis and inheritance in 

 experimental reproduction. II. Physiological dominance of anterior 

 over posterior regions in the regulation of Planaria dorotocephala. 

 Jour. Exp. Zool., vol. 11, no. 3. 



1911 f Studies on the dynamics of morphogenesis and inheritance in 

 experimental reproduction. III. The formation of new zooids in 

 Planaria and other forms. Jour. Exp. Zool., vol. 11, no. 3. 

 Child, C. M., and McKie, E. V. M. 1911 The central nervous system in terat- 

 ophthalmic and teratomorphic forms of Planaria dorotocephala. Biol. 

 Bull., vol. 22, no. 1. 



