DOMINANCE IN RECONSTITUTION 355 



SCALE OF ORGANIZATION IN OTHER RECONSTITUTIONS AND 

 AGAMIC REPRODUCTIONS 



Evidences of a very considerable range in scale of organization appear 

 in many organisms, but only a few further examples are noted here. Pieces 

 of Stentor about 1/27 of the volume of the original individual reconstitute 

 complete individuals (F. R. Lillie, 1896); but whether minimal size of 

 piece capable of such reconstitution varies with level of body from which 

 it is taken is not known. According to Morgan (1901c?), however, the 

 peristome is "too large" in individuals reconstituting from anterior pieces, 

 "too small" in those from posterior pieces. These differences are evi- 

 dently expressions of the longitudinal gradient shown by other methods 

 to be present. As in planarian pieces, these differences gradually decrease, 

 and with feeding the usual proportions may be attained. 



Certain nemerteans show a very wide range of scale of organization in 

 reconstitution. Coe regards the regenerating nemertean head region as 

 dominant and inducing the further reorganization of the piece. '^ In an- 

 nelid reconstitution a wide range in scale of organization also appears. 

 In most annelids capable of anterior reconstitution this is only in part 

 regeneration, no more than a certain number of segments being regen- 

 erated, even though more were removed, the intervening parts being 

 formed by reorganization of old segments into segments characteristic of 

 more anterior levels. In some of the more transparent microdrilous oligo- 

 chetes this reorganization can be observed in the living animal, and in 

 some other cases its occurrence has been noted, but in many studies on an- 

 nelid reconstitution the question is not considered. The number of segments 

 reorganized may vary greatly in some species, but experimental analysis 

 of the extent of reorganization in relation to dominance of the regenerating 

 anterior regions is largely lacking. The case of Sahella is of special interest 

 because reorganization of "abdominal" into "thoracic" segments in re- 

 constitution is directly visible, since the two regions differ morphologi- 

 cally, and also because the reorganization may take place in relation to a 

 level of section before head regeneration; and in some cases reorganization 

 of a few segments occurs anteriorly from a posterior level of section. Evi- 

 dently the activation following anterior section, and sometimes that fol- 

 lowing posterior section, is sufficient to initiate the reorganization of other 

 segments, that from the posterior section being on a small scale, as might 

 be expected, since it opposes the polarity present. Evidently the reorgani- 



'5 For data bearing on the question of scale in nemertean reconstitution see Nusbaum und 

 Oxner, 1910, iqii, 1912; Davydov, 1915; Coe, 1929, 1930, 1932, 1934a, b. 



