GENERAL INTRODUCTION 5 



longitudinally into two pieces, the pieces die. If only a part of the 

 worm is split longitudinally and one part removed, the latter will be 

 regenerated from the remaining part. 1 Several contemporaries of 

 Spallanzani also made experiments on the earthworm. 2 



Spallanzani found that a tadpole can regenerate its tail ; and if a 

 part of the new tail is cut off, the remaining part will regenerate 

 as much as is lost. Older tadpoles regenerate more slowly than 

 younger ones. If a tadpole is not fed, it ceases to grow larger, 

 but it will still regenerate its tail if the tail is cut off. 3 Salamanders 

 also regenerate a new tail, producing even new vertebrae. If a leg 

 is cut off, it is regenerated ; if all four legs are cut off, either at 

 the same time or in succession, they are renewed. If the leg is 

 cut off near the body, an imperfectly regenerated part is formed. 

 Regeneration of the legs was found to take place in all species of 

 salamanders that were known to Spallanzani, but best in young 

 stages. In full-grown salamanders, regeneration takes place more 

 promptly in smaller species than in larger ones. Curiously enough, 

 it was found that if the fingers or toes are cut off, they regenerate 

 very slowly. If the fingers of one side and the whole leg of the 

 opposite side are cut off at the same time, the leg may be regen- 

 erated as soon as are the fingers of the other side. A year is, how- 

 ever, often insufficient in some forms for a leg to become fully 

 formed. If an animal is kept without food for two months after 

 a leg has been cut off, the new leg will regenerate as rapidly as in 

 another salamander that has been fed during this time. If the 

 animal is kept longer without food, it will decrease in size, but 

 nevertheless the new leg continues to grow larger. Occasionally 

 more toes or fewer toes than the normal number are regenerated ; 

 but as a rule the fore leg renews its four toes, and the hind leg 

 its five toes. 



In one experiment, all four legs and the tail were cut off six times 

 during the three summer months, and were regenerated. Spallan- 

 zani calculated that 647 new bones must have been made in the new 

 parts. The regeneration of the new limbs was as quickly carried out 

 the last time as the first. Spallanzani also found that the upper and 

 lower jaws of salamanders can regenerate. 



If the tentacles of a snail or of a slug are cut off, they are renewed ; 

 and Spallanzani found that even if the entire head is cut off a new 

 one is regenerated. Also other parts of the snail, as the foot, or the 



1 There is some doubt in regard to this statement of Spallanzani's. In a letter to Bonnet 

 he denies that this takes place in the earthworm. 



2 Spallanzani refers to the work of Ginnani, Vandelli, Vallisneri. 



8 He found that the legs of the tadpole of the frog, and of two species of toads, also have 

 the power of regeneration. 



