CH. xxiv. BONNET AND SPALLANZANI. 201 



wards, so as to bring the little mouths, or stomata, close to 

 the sponge, and enable them to drink in the water. In this 

 way a plant will always find out the best way of growing so 

 as to get as much sun and food as it can. Many curious 

 facts of this kind were published in Bonnet's work on the 

 ' Use of the Leaves of Plants/ but what I wish now particu- 

 larly to relate to you are his experiments upon animals and 

 the regrowth of limbs which had been cut off. 



It had long been known that very simple organisms, such 

 a,s polyps, may be cut in pieces, and each part will live and 

 become a perfect creature ; but no one thought it possible 

 that any of the more complicated living beings could be 

 treated in this way. Bonnet, however, and the famous 

 Italian naturalist Spallanzani (1729-1799) proved by a great 

 number of experiments that tails, legs, and even heads will 

 grow again in some animals after they have been cut off. 

 The garden-worm, for example, is an animal with many 

 organs : it has numerous bristles, which serve as feet, it has 

 arteries and veins, nerves, and organs of digestion, and a 

 mouth ; yet Bonnet found that a worm if cut in pieces would 

 grow a new head or a new tail, and, what was still more 

 curious, in some rare cases it grew the head on the end where 

 the tail had been before ! 



Spallanzani went even farther than this, for he experi- 

 mented on snails. Now the common garden snail has a 

 head with four horns, moved by very complicated muscles, 

 and two of these horns have eyes at the end of them ; more- 

 over it has a mouth, with teeth and a tongue. Spallanzani 

 cut off first the horns with eyes, and afterwards the mouth 

 and tongue, and found that the snail had power to re-grow 

 them all. He then tried upon aquatic salamanders, which 

 resemble our newts, or efts. These creatures have red blood 



