CONTROL OF HEAD FORMATION IN PLANARIA 11 



ment the required number of worms of as nearly as possible the 

 same size were selected at the same time from a single stock pan. 

 Tests show that under such conditions two groups of animals 

 so selected do not differ appreciably in rate of oxygen consump- 

 tion. Nutritive conditions were controlled as the experiments 

 required by withholding the food from the pan from which the 

 selection was to be made for the designated period of time. 



The narcotics used were a number of common anesthetics, 

 chloroform, ether, chloretone, chloral hydrate, ethyl alcohol, 

 and, in a few cases, methyl, normal propyl, and iso-butyl alco- 

 hols. When obtainable, Kahlbaum's and Squibb's products 

 were used. All solutions were made up freshly just before 

 using. The concentrations mentioned in the data are only 

 approximate; although corrected for the specific gravity of the 

 anesthetic and made up as carefully as possible, no attempt was 

 made to determine the molecular concentrations more accurately. 



The nature of the experiments divides them into two groups : 

 those concerned with head frequency after short periods of ex- 

 posure of the freshly cut pieces to relatively strong solutions of 

 the anesthetics and with the rate of oxygen consumption during 

 such exposure, and those concerned with the head frequency of 

 pieces kept in more dilute solutions of the anesthetics during 

 the entire period of regeneration and the effects of such solutions 

 on the rate of oxygen consumption of the pieces during this 

 period of time. 



In general, for the head-frequency experiments one hundred 

 or more worms of as nearly as possible identical size were se- 

 lected from the same stock pan at the same time. Fifty of 

 them served as controls and the anterior zooids were cut into 

 A, B, and C pieces (fig. 3), the heads and posterior zooids being 

 discarded. The pieces as soon as cut were dropped with a pi- 

 pette into separate Erlenmeyer flasks of 500 cc. capacity filled 

 with well-aerated water, A pieces in one flask, B in another, 

 and C in another, each flask thus receiving fifty pieces from the 

 same region of the animals. The flasks were then stoppered; 

 a small air space was left under the stopper to allow for the 

 changes in volume of the contents with temperature changes. 



