2OO C. M. CHILD AND L. H. HYMAN. 



often show a purely basipetal gradient, even after the stalk is 

 distinguishable morphologically (p. 194), it is at least possible, 

 that in this case the stalk had not attained complete specializa- 

 tion as a contractile region. 



In all other cases of full grown attached individuals of H. oli- 

 gactis more or less contraction occurred in the stalk, and the sec- 

 ondary gradient 01 gradients appeared according as the secondary 

 disintegration began at the foot (Figs. 47-50) or above it (Figs. 

 51-54) and the acropetal gradient in all cases extended at least 

 to the middle of the body (Figs. 50, 54) and often farther api- 

 cally. 



While these observations on the susceptibility of attached, 

 quiescent animals indicate that the stalk of H. oligactis is more 

 highly specialized than that of the other species, at least as re- 

 gards its sensitiveness, they do not prove that it is permanently 

 a region of high susceptibility. 



THE GRADIENTS IN DETACHED AND RECENTLY ATTACHED 

 ANIMALS WITHOUT SPECIAL EXCITATION. 



In all three species the activity of the stalk is usually greater 

 in the detached than in the attached animals even without any 

 special external excitation, and the early appearance of disinte- 

 gration at the foot (Figs. 55-57, H. oligactis) or in the stalk above 

 it (Figs. 58-60, H. vulgar is) is the characteristic result as in at- 

 tached animals with stalk contraction (Figs. 36-42 and 47-54). 

 Here again KNC is the most satisfactory agent among those 

 used, although the lower concentrations of anesthetics and dyes 

 give the same results. In general the more active or more 

 V strongly contracted the stalk, the earlier it begins to disintegrate. 

 In H. oligactis cases like 61-64 are not infrequently seen. Here 

 the stalk is strongly contracted and the body progressively less 

 contracted from the base apically, and disintegration begins in 

 the stalk even earlier than the tentacles and progresses acropet- 

 ally to the hypostome, i. e., complete reversal of the gradient 

 occurs, except in the tentacles. Such reversal has not been ob- 

 served in the other species. 



Rarely, however, detached individuals of H. viridissima and 

 H. vulgaris remain quiescent with extended stalk and show the 



