DYNAMICS OF MORPHOGENESIS 195 



Turning to another line of experiment, we find that in pieces of 

 a given size from a given stock of worms, the different types of 

 head show different resistances by the direct method. In general 

 the normal head shows the lowest resistance, that of the terato- 

 phthalmic head is somewhat higher and the increase continues 

 through the teratomorphic and anophthalmic to the headless 

 type (for a description of these different types of head, see Child 

 '11 b '11 c). I have already shown (Child '11 c '12 a) that we 

 can induce the appearance of the more abnormal types of head in 

 place of the less abnormal by decreasing the rate of reaction in 

 the head-forming regions and can bring about changes in the 

 opposite direction by increasing the rate of reaction in this region. 

 According to the results of the direct method of determining the 

 resistance, the normal head shows the highest rate and from this 

 the rate decreases through the various forms to the headless tj'pe. 

 Here then the two lines of experiment — production of the abnormal 

 types of head with the aid of external factors and determination 

 of the physiological resistance of the different types — are in com- 

 plete agreement and we cannot doubt that the difference in resist- 

 ance in the different types is determined by the differences in 

 rates of reaction. 



It remains now to mention a widely different line of evidence 

 which serves to confirm the results of the resistance method. 

 Dr. Tashiro, an assistant in Dr. A. P. Mathews' laboratory at 

 the University of Chicago, has recently devised an exceedingly 

 delicate apparatus which makes it possible to determine and com- 

 pare the amounts of C02-production in small or nearly quiescent 

 organisms or pieces of tissue. Dr. Tashiro has been kind enough 

 to make a number of comparative tests of C02-production in indi- 

 viduals and pieces of Planaria under different conditions ; in every 

 case, the results obtained are parallel to my own, obtained with 

 KCN and alcohol. Animals or pieces which by the direct method 

 show a lower resistance show in this apparatus a higher rate of 

 COo-production. Direct comparisons by means of this apparatus 

 are limited to animals and pieces of approximately the same size, 

 so that as far as my own results concern animals and pieces of 

 different size they cannot be directly confirmed in this way. 



