RECONSTITUTIONAL PATTERNS IN EXPERIMENT 381 



tive, it inhibits hydranth development to a greater or less degree at the 

 distal end of the piece (Child, 1935). Development of a base at the distal 

 end of the piece involves complete reversal of polarity; in those forms the 

 dye-reduction gradient is also reversed in direction. Development of a 

 base at the proximal end of the piece also gives evidence of the dominance 

 of the graft hydranth, for it occurs in much higher frequency than in con- 

 trol pieces without graft hydranth. A similar dominance of the hydra 

 bud has been repeatedly observed. If the parent body is cut off a short 

 distance distal to a bud or if a bud forms soon after section, reconstitution 

 is often inhibited, and the bud may become the apical region of the indi- 

 vidual (Weimer, 1938; Rulon and Child, 1937). 



Reversal of polarity in short pieces of hydroids, planarians, and an- 

 nelids grafted in inverse position on longer pieces^^ has usually been re- 

 garded as resulting from an action of the longer on the shorter component. 

 In view of the evidence for independence of the dominant region it ap- 

 pears improbable that any such action of the longer component is involved 

 in development of an apical region or head on the basal or posterior end 

 of the short piece grafted to the longer. The development probably oc- 

 curs at the free end simply because the grafted end is not dominant. The 

 case does not appear to be essentially different from development of hy- 

 dranth or head on the proximal or posterior end of a completely isolated 

 piece that becomes bipolar. On the other hand, development of a basal 

 or posterior part from the distal or anterior end of a short piece grafted 

 to a longer in inverse position is undoubtedly determined by the domi- 

 nance of the longer component. 



The work of Moretti (1911), Gebhardt (1926), and Goetsch (1929) has 

 given evidence of determination of new axes in planarians by grafts, and 

 more recent experiment has demonstrated conclusively the dominance and 

 inductive capacity of both homoplastic and heteroplastic grafts from the 

 region of the cephalic ganglia and from certain other regions."" Here only 

 a few of the varied results can be presented. Postcephalic parts do not 

 develop from isolated heads, even when entire ; and small pieces from the 

 ganghonic region with cut surfaces on all sides, such as have been used 



'5 E.g., Peebles, igoo; King, 1901; L. V. Morgan, 1906; Ruttloff, 1908; Leypoldt, 1910; 

 Korschelt, 1927-31, 1929. 



'^Santos, 1929, 1931, homoplastic, Dugesia { = Enplariaria) dorotocephala and D. tigrina, 

 heteroplastic between these species; Okada and Sugino, 1934, 1937, and Sugino, 1938, homo- 

 plastic, Planaria gonocephala, a Japanese species known by that name; J. A. Miller, 1938, 

 heteroplastic, D. dorotocephala, D. tigrina, and D. tigrina novangliae. 



