1 88 C. M. CHILD AND L. H. HYMAN. 



differences in specialization between stalk and body appear in 

 general to be greater in H. oligactis than in the other two species. 



Whatever its degree of development in full-grown individ- 

 uals, the stalk is not present in young buds (Figs. 12, 14) nor 

 in the earlier stages of the regulatory development of pieces 

 of any of the three species, but is a secondary outgrowth from, 

 or modification of the basal region of the column arising compara- 

 tively late in the development of buds (Fig. 13) and of pieces 

 undergoing regulation. Not infrequently buds become detached 

 from the parent before any considerable development of the stalk 

 occurs, and in such cases the stalk develops later in the young, 

 independently attached individual. In its early stages the stalk 

 is very short, much shorter than the body and is not appreciably 

 more contractile than other regions but both its length and its 

 contractility increase until it is commonly somewhat longer than 

 the body in well-extended animals of H . oligactis (Fig. 7) and shor- 

 tens more than the body in extreme contraction (Figs. 10, ii). 



The stalk is evidently then a more or less specialized region 

 or organ arising at a late stage of development and functioning 

 in connection with the sessile habit as an organ of extension and 

 contraction. This being the case, it is also evident that the 

 process of budding in hydra takes place at or near the basal end 

 of the body proper, and in this connection it may be suggested 

 that, while the specialization of the stalk is not so great as to 

 prevent its dedifferentiation and regulatory development into a 

 complete individual when it is physically isolated from the 

 parent body, yet it is so much greater than that of the basal re- 

 gion of the body that the buds arise from the latter region rather 

 than from the basal end or any other level of the stalk. 



As regards behavior, both the tentacle and the column repre- 

 sent to a certain degree a relation of dominance and subordina- 

 tion. Under natural conditions the more distal regions of the 

 tentacles must be more frequently stimulated than regions near 

 the base, consequently contraction of the basal region of the ten- 

 tacle is more likely to occur as the result of stimulation of a re- 

 gion distal to it than as the result of direct stimulation from with- 

 out. While no extensive investigation of the problem has been 

 undertaken simple experiments on mechanical stimulation with 



