408 C. M. CHILD 



'18), and further data bearing on this point are presented below; 

 third, normal heads and often biaxial heads may develop on 

 pieces so short that the whole substance is used up in the 

 development of the head or heads. Taking all the facts into 

 account, it is evident that while the amount of nutritive material 

 may play some part in determining head-frequency, it is not 

 the primary factor in determining the differences between large 

 and small animals. 



HEAD-FREQUENCY IN RELATION TO NUTRITIVE CONDITION 



It has been shown that starvation in P. dorotocephala is ac- 

 companied by various changes in physiological condition. The 

 susceptibility of body wall and ectoderm (probably also of paren- 

 chyma) increases from the beginning of starvation, that of the 

 alimentary tract in the later stages (Child, '15 a, chap. VII, '19 c). 

 Carbon dioxide production and oxygen consumption decrease in 

 the early stages of starvation, undoubtedly because of the decrease 

 in activity of the alimentary tract in the absence of food, but later 

 increase (Child, '19 a; Hyman, '19 a, and in advanced stages of 

 starvation the animal may have a much higher rate of respiration 

 than at the beginning of starvation, and this rate is still further 

 increased by renewed feeding. As regards rate of respiration and 

 susceptibility, the starving animal apparently becomes physiolog- 

 ically younger, and with renewed feeding may again begin 

 growth and progressive development from a stage physiologically 

 earlier than that at the beginning of starvation. It is of interest, 

 in the light of these facts, to determine the effect of starvation 

 upon head-frequency, and data along this line are given in 

 table 2. 



Table 2 shows in all cases that the head-frequency in pieces 

 from starved animals is less than in fed animals, even when of 

 the same size. 



Certain points in the various series demand brief notice. So 

 far as actual difference in percentage is concerned, it will be ob- 

 served that the effect of starvation is in general most conspicuous 

 in the most anterior pieces (A) and in series 327 in the long pieces 

 (X). The differences in these cases are entirely or almost en- 



