126 Animal Life and Intelligence. 



a dozen times. After such mutilation, no part of the eye 

 remains, though the stump of its nerve is, of course, left ; 

 still the perfect organ is reconstructed again and again, as 

 often as the tentacle is removed. The cells at the cut end 

 of the nerve-stump divide and multiply, as do also those of 

 the surrounding tissues, and the growing nerve terminates 

 in an optic cup, as it did previously under the influences of 

 normal development before the mutilation. Here we have 

 phenomena analogous to, and in some respects more com- 

 plex than, those which are seen in the regenerative process 

 in hydra. It is well known, however, that, in the case of 

 higher animals, in birds and mammals, this power of 

 regenerating lost parts does not exist. When a bone is 

 broken, osseous union of the broken pieces may indeed take 

 place ; and in flesh-wounds, the gash is filled in and heals 

 over, not without permanent signs of its existence, as may 

 often be seen in the faces of German students. But beyond 

 this there is normally no regeneration. The soldier who 

 has lost an arm in battle cannot return home and in quiet 

 seclusion reproduce a new limb. That which seems to be 

 among lower animals a well-established law of organic 

 growth does not here obtain. This is probably due to the 

 fact that the higher histological differentiation of the tissues 

 in the more highly developed forms of life is a bar to 

 regeneration. In their devotion to special and minute 

 details of physiological work, the cells have, so to speak, 

 forgotten their more generalized reproductive faculties. 

 In any case, however the fact is to be explained, the 

 higher organisms have in many cases almost completely 

 lost the power of regenerating lost parts. But this loss of 

 the regenerative power in the more highly differentiated 

 animals does not alter or invalidate the law of organic 

 growth we are considering. The law may be thus stated : 

 Whenever, after mutilation, free growth of the mutilated surface 

 occurs, that growth is directed in such lines as to reproduce 

 the lost part and restore the symmetrical integrity of the 

 organism. This is a matter of heredity. And we may 

 regard the hereditary reconstructive power as residing 



