PROBLEMS OF MODERN SCIENCE 



most complex actions even of the highest animals 

 as mere reflexes, of exactly the same nature as 

 the tropisms and tactisms of the lower forms of 

 life and equally explicable as purely mechanical 

 effects of stimulation. The well-known work 

 of Hans Driesch, on the other hand, is frankly 

 vitalistic in its interpretations, but we must leave 

 the discussion of his " Entelechy," along with 

 that of Bergson's " Elan vital," to the philo- 

 sophers. 



The study of animal behaviour merges almost 

 imperceptibly into Experimental Morphology and 

 Embryology. In this direction a wide prospect 

 has been opened up during the last few decades, 

 and one which has attracted many of our ablest 

 biologists. Some of the earliest experiments in 

 this field were those on the regeneration of lost 

 parts, whereby a mutilated organism is able to 

 make itself whole again. Developed to a surpris- 

 ing extent both amongst plants and amongst the 

 lower animals, this power gradually diminishes 

 as we ascend the vertebrate series, until in man, 

 unfortunately, it almost reaches a vanishing point. 

 Even amongst the lower vertebrates, however, 

 limbs may be removed and regenerated almost 

 ad libitum^ and the experimental regeneration of 

 the lens of the newt's eye from the margin of the 

 iris seems to defy any purely mechanistic expla- 

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