394 BIOLOGY: GENERAL AND MEDICAL 



to regenerate just the same. It takes about as long 

 for the perfect regeneration of the fingers or toes as for 

 an entire limb. If a limb be amputated too close to the 

 body, no regeneration takes place, though the wound 

 heals. In one experiment, Spallanzani amputated all 

 four legs and the tail of a salamander six times and saw 

 them all regenerate six times during the three summer 

 months. He also found that the upper and lower jaws of 

 salamanders can regenerate. Lessona found that terres- 

 trial salamanders cannot regenerate lost parts, though 

 aquatic species of the same genus can do so. Extend- 

 ing these experiments still further, Spallanzani found 

 that snails can regenerate amputated tentacles and 

 that certain of them can regenerate the entire head, 

 collar, or foot. 



Since the time of Spallanzani much experimental 

 work has been done and many facts added to the knowl- 

 edge of the subject, though we are still greatly in need 

 of illumination concerning the general principles by 

 which what is known can be correctly correlated. 



We now know that lizards frequently lose their tails 

 and regenerate them, also that the animals seem to know 

 that they can do so, for when caught they unhesitat- 

 ingly snap them off to escape. Though it can re- 

 generate the tail, a lizard cannot regenerate the limbs 

 or even the toes. Newts not only regenerate the tail 

 and limbs, but also the eyes. Crustaceans crabs and 

 lobsters regenerate legs, fighting claws, and sometimes 

 antennae and eyes. Certain arthropods myriapods, 

 arachnids, and a few insects are able to regenerate 

 lost limbs, but this power is restricted to a few species of 

 scattered groups. 



In all of these cases certain facts regarding the regen- 

 erative power must be noted. Thus, the extent of the 

 mutilation determines whether the injured animal shall 

 die or live as well as whether the wound shall simply 

 heal or shall regenerate. In speaking of the salamander's 

 legs it has already been remarked that though they may 



