MUTILATION AND REGENERATION 



373 



such facts as are known, and to realize the difficulties 

 in the way of accurately comprehending them. 



I. The mutilated organism restores its symmetry by a 

 rearrangement of its substance and recovers its size by 

 subsequent growth. 



This is seen in lowly organisms only. Thus, when the 

 protozoan Stentor cceruleus is cut transversely into 

 several segments, each transforms itself into a more or 



Fia. 139. Stentor coeruleus. a, Cut into three pieces; b, regeneration of 

 anterior piece; c, regeneration of middle piece; d, regeneration of posterior piece. 

 (After Gruber.) 



less perfect diminutive of the original in the course of a 

 few hours and is then ready to grow to its normal size. 



A similar adjustment is seen in Hydra. When this 

 organism is transversely cut, the anterior half lengthens 

 and develops a new base, the posterior half also lengthens 

 and develops new tentacles, so that two new hydras are 

 formed. If a fragment be cut out of the centre of a 

 hydra by two parallel transverse incisions, the ends 

 gradually close, until a hollow prolate spheroid is formed. 



