194 C - M - CHILD. 



bility to cyanide of a piece immediately after isolation is much 

 greater than that of the corresponding region of the body in an 

 uninjured animal of the same age and physiological condition. 

 This greater susceptibility of the piece means that it has been 

 stimulated by the act of isolation. After this sudden rise its 

 susceptibility to cyanide decreases gradually during twenty-four 

 hours or more and in small pieces may fall below that of corre- 

 sponding regions in the uninjured animal (Child, 'i3&). This 

 decreasing susceptibility means that the rate of metabolism in 

 the piece is gradually decreasing as the stimulation resulting from 

 section gradually disappears. 



The cyanide method shows further that the degree of stimula- 

 tion increases as the size of the piece isolated decreases and also 

 as the distance of the level of the piece from the head region 

 increases. In other words smaller or more posterior pieces are 

 more stimulated by the act of section than larger or more anterior 

 pieces. And finally pieces cut from worms at a higher tempera- 

 ture w r ithin certain limits are more stimulated and show a 

 greater increase in rate than pieces from worms at a lower 

 temperature. 



These relations between the degree of stimulation of pieces 

 and the factors of size of piece and region of the body and various 

 external conditions have been worked out completely for Planaria 

 dorotocephala and the data will be presented in full elsewhere. 

 Sufficient w r ork has been done on P. velata to show that the 

 relations are essentially the same as in P. dorotocephala, but since 

 the work on the latter species furnishes the foundations for the 

 conclusions and since the data for that species are in more com- 

 plete form and will be published in a short time the evidence for 

 the above statements concerning the degree of stimulation in 

 pieces of P. velata is not presented in detail. 



So far then as region of the body, size of piece and temperature 

 are concerned the frequency of encystment of pieces in P. velata 

 runs parallel to the degree of stimulation by the act of section. 

 Apparently the more the piece is stimulated by section the more 

 likely it is to encyst. 



The process of encystment in this species consists in the rapid 

 secretion over the surface of the body of a thick slime which 



