424 



BIOLOGY: GENERAL AND MEDICAL 



Much experimental manipulation of this kind has 

 been performed with hydras. Trembly, Watzel, King, 

 Morgan, and others have subjected these animals to a 

 variety of amputations and abnormal appositions, and 



FIG. 147. Regeneration in hydras, a, Hydra split in two hanging vertically 

 downward: later the halves completely separated; B, two posterior ends united 

 by oval surfaces; B l , same: its regenerated two heads, each composed of parts of 

 both pieces. B 2 , absorption of one piece leading to a later separation of halves; 

 C, two posterior ends united by oblique surfaces: later one piece partially cut 

 off, as indicated by line; C 1 , later still, two heads developed, one at M, the other 

 at N; D, similar experiments in which only one head develops at M; E, five 

 pieces united as shown by arrows. Four heads regenerated, one being composed 

 of parts of two pieces. (Morgan after King.) 



found that the force of polarity is easily set aside. Thus 

 the organisms can be made to .unite either by their 

 oral or aboral ends. Several individuals deprived 

 of the oral ends and tentacles can also be united and 

 very long-bodied individuals produced. In one case 



