132 C. M. CHILD 



type at low temperature (fig. 45) practically all regulation beyond 

 wound-closure has been inhibited. The important feature of 

 the series for present purposes is the development of heads at a 

 temperature which practically inhibits the development of the 

 posterior end. 



In general the temperature experiments give results similar 

 to those obtained with anesthetics and KCN. They indicate the 

 existence of an antero-posterior dynamic gradient. Head-forma- 

 tion and the development of a small pharynx may occur at a 

 temperature which practically inhibits development of the pos- 

 terior end. The low temperature affects pharynx-formation 

 more than head-formation and the development of the posterior 

 end more than either. 



The results with different temperatures are less extreme than 

 those obtained with KCN and the anesthetics, but they are of 

 the same character and since we know that the changes in organ- 

 isms produced by different temperatures are primarily quantita- 

 tive, they serve to confirm the conclusion that the effects of the 

 other external agents are likewise primarily quantitative. 



4. Other experimental conditions 



"With various other experimental conditions the results are essen- 

 tially similar to those already described. In pieces from worms 

 in extreme stages of starvation regulation at the posterior end is 

 retarded to a greater extent than at the anterior end, the basis 

 of comparison being of course well fed worms. Absence of food 

 undoubtedly results sooner or later in a decreased rate of metab- 

 olism (Child, '11 b) and in pieces with this decreased rate the 

 regulatory morphogenetic development at the posteirior end is 

 retarded or inhibited to a greater extent than at the anterior end. 



Similarly the presence of metabolic products of Planaria in the 

 water undoubtedly decreases the rate of metabolism and the effect 

 on regulatory morphogenesis is similar to that of starvation or 

 low temperature, though it may be greater and in extreme cases 

 approaches that obtained with the anesthetics. In the second 

 paper of this series some of the results obtained with metabolic 

 products in the water were described in another connection (Child, 



