THE KECONSTITUTIOX OF ISOLATED PIECES 



"3 



W 



character of the head departs from normal. 

 In pieces of the same length and from the 

 same region the size of the head and the 

 length of the pharyngeal and prepharyn- 

 geal region are less in teratophthahnic and 

 teratomorphic than in normal animals and 

 less in anophthalmia than in teratomorphic 

 or teratophthahnic forms. Between the 

 teratophthahnic and teratomorphic forms 

 the differences in this respect are not very 

 great except when opposite extremes of the 

 two types are compared. 



That the production of a normal or 

 nearly normal animal from a piece requires 

 more energy than the production of a head- 

 less form is indicated by the fact that a 

 much greater amount of reduction occurs 

 in the former than in the latter case. 

 Moreover, in a given lot of pieces it is 

 possible by means of external conditions 

 such as temperature, low concentrations of 

 narcotics, etc., whose effect is primarily 

 quantitative rather than quahtative, to 

 determine experimentally within wide 

 limits which of the five forms shall be pro- 

 duced (ChUd, 'lib, '12b). Experiments of 

 this kind have demonstrated that aU four 

 forms from the teratophthahnic to the 

 headless are what might be called sub- 

 normal, i.e., they are due to various degrees 

 of retardation or inhibition of the dynamic 

 processes (Child, '116, '14a, '146). .\nd, 

 finally, after their development is com- 

 pleted, the normal head shows in general 

 a higher susceptibility than the teratoph- 

 thahnic and teratomorphic, and these a higher susceptibihty than 

 the anophthabnic. 



Fig. 24. — Body-outline 

 of Planaria dorotocephala, 

 indicating levels of section. 



