280 ELLINOR HELENE BEHRE. 



Child. It is a great pleasure to me to have this opportunity to 

 express my thanks to Professor Child, not only for the stimulus 

 of his ideas and for his valuable suggestions, but for his kindness 

 in placing at my disposal certain unpublished data from his own 

 experiments concerning the effect of temperature on head-fre- 

 quency and head-form in the regeneration of pieces of Planaria. 

 My warm thanks are due to Dr. L. H. Hyman, of the Department 

 of Zoology of the University of Chicago, for her keen and 

 thoughtful criticism, constant encouragement, and constructive 

 advice. I wish further to acknowledge my deep indebtedness 

 to other colleagues and to the friends whose help during these 

 three years has made effort easy. 



II. MATERIAL, GENERAL METHODS AND TERMINOLOGY. 



The material used for these experiments was Planaria doroto- 

 cephala, one of the triclad turbellarians, the same species used 

 extensively by Child ('n, a, b, c, etc.) in his earlier studies on the 

 axial metabolic gradient. It is found in the springs that feed 

 into swamps a short distance back from the banks of the Fox 

 River, near Cary, 111. The material lends itself very well to 

 temperature experiments; for though its natural habitat is in 

 waters of relatively low temperature, the stock lives readily in 

 the laboratory at 17 C., and can continue to exist to all intents 

 normally in temperatures varying from somewhat over 30 C. 

 to at least as low as 4. The temperatures employed all lay 

 well within these limits, between 30 and 5. The stock was 

 collected and brought into the laboratory at intervals during 

 the time covered by the experiments, and was fed on liver three 

 times weekly (the frequency which has been found necessary to 

 maintain growth) throughout the period. 1 With this treatment 

 the stock maintains itself in normal condition. 



For the experimental work three general temperatures were 

 employed, approximately 10 apart; that of the refrigerator 

 ranging between about 8 and 10 C., that of the general labora- 

 tory, 1 8 to 20; and that of a warm chamber, between 27 and 



1 During a part of the time high temperature stock was fed mo:e often, as it 

 \vas found that metabolism is so rapid at raised tmperature on tri -weekly feedings 

 that the worms not only may not grow but may even decrease in ske. 



