40 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



branches acropetally (Fig. 14, B). Meanwhile the original apical region 

 of the main axis and the new multiaxiate individual which has developed 

 from the proximal cut end may grow and give rise to new hydranths; evi- 

 dently they are able to live at the expense of lower axial levels (Fig. 14, C). 

 A gradient pattern is evident in this whole series of events. The rate of re- 

 constitution decreases basipetally in the whole and in each axis; as the 

 animals starve in the laboratory, lower axial levels are used in maintaining 

 higher levels. Possibly differential tolerance to laboratory conditions is 

 also involved (see chap. v). The reconstituted multiaxiate individual at 

 the proximal end undoubtedly represents younger, more intensely active 

 tissues than the old coenosarc, perhaps even more active than the original 

 apical region, and so is able to persist and grow for a longer time than any 

 other part. A few unpublished experiments with P. tiarella indicate that 



TABLE 2 



a similar gradient exists in that form, though less regular, as the less regu- 

 lar growth form of the species would suggest. 



A gradient in rate of reconstitution in Obelia has been noted by Billard 

 (1904) and Lund (1923a) and in Eudendrium by Goldforb (1907). In the 

 sessile scyphozoan Haliclystus auricula (Child, 1933^) and in the actinians 

 Cerianthus solitarius (Child, 19030), C. aestuarii (Child, 1908), and Haren- 

 actis attenuata (Child, 1909a) a similar gradient in rate occurs. Table 2 

 gives tentacle length for Harenactis pieces at different times after section 

 at the five body-levels indicated in Figure 15, ^. The tentacles from the 

 more distal levels appear earlier, and in general grow more rapidly and 

 attain greater length, than those of levels farther proximal. In the last 

 column, 26 days, the tentacles of the a-pieces have begun to decrease in 

 length, as all do sooner or later in animals kept without food and not per- 

 mitted to burrow in sand. In these pieces the aboral ends were intact, and 

 consequently the pieces differed greatly in length; but other experiments 



