Physiological Morphology 



95 



are exhibited by the same animal. If we cut out a sufficiently 

 large piece of the stem of Tubularia mesembryanthemum, and 

 place it in the bottom of a dish of water, 

 carefully protected from jarring, the ante- 

 rior end of the piece gives rise to a new 

 polyp, the posterior end to a root; but if 

 we hang up the stem in such a way that the 

 posterior end does not touch the surface of 

 the glass, and is sufficiently provided with 

 oxygen, this end, too, produces a polyp, and 

 we have a true case oi heteromorphosis 

 (Fig. 32). In all cases the polyp at the oral 

 end is formed first, and a relatively ong 

 time (one or more weeks) elapses before 

 the aboral polyp is formed. Under one con- 

 dition, however, I could cause the stem to 

 form a polyp at the aboral as quickly as at 

 the oral end, namely, by inhibiting or re- 

 tarding the formation of the oral polj^j. 

 This could be done readily by diminishing 

 the supply of oxygen at the oral end. In 

 such cases the aboral polyps were produced 

 almost as quickly as the oral polyps.' 



Fig. 



III. 



THE MECHANICS OF GROWTH IN 

 ANIMALS 



In order to arrive at an explanation 

 of the phenomena of organization we must 

 ask what the physical forces are that 

 determine the formation of a new organ. 

 We know that the ultimate sources of 

 energy for all the functions of living bodies 



32. — Hetero- 

 morphosis in Tubula- 

 ria. From natm:e. 

 The normal Tubularia 

 ends at one end in a 

 stolon, at the other 

 in a head or polyp. 

 If a piece o 6 is cut 

 out and suspended in 

 water a new head or 

 polyp c and d is formed 

 at both ends. We 

 can thus produce an 

 animal which termi- 

 nates in a head at 

 both ends of its body ; 

 while in Fig. 28 an 

 animal was represent- 

 ed which ended at 

 both ends in a stolon 

 or foot. 



1 It was foimd later independently by both Godlewski and myself that if we 

 ligature the stem of a Tubularian the polyps at both ends are formed simultane- 

 ously (1912). 



