6 RE GENERA TION 



collar, may be regenerated. The head of the slug, it was found, 

 regenerates with more difficulty than does that of the snail. 



These justly celebrated experimentsof Trembley, Reaumur, Bonnet, 

 and Spallanzani furnished the basis of all later work. Many new facts, 

 it is true, have been discovered, and in many cases we have penetrated 

 further into the conditions that influence the regeneration, but many 

 of the important facts in regard to regeneration were made known by 

 the work of these four naturalists. 



SOME FURTHER EXAMPLES OF REGENERATION 



So many different phenomena are included at the present time 

 under the term " regeneration," that it is necessary, in order to get a 

 general idea of the subject, to pass in review some typical examples 

 of the process. 



The regeneration of different parts of the salamander shows some 

 characteristic methods of renewal of lost parts. If the foot is cut off 

 a new foot is regenerated; if more than the foot is cut off, as much is 

 renewed as was lost. For instance, if the cut is made through the 

 fore leg, as much of the fore leg as was removed, and also the foot, 

 are regenerated ; if the cut is made through the upper part of the 

 leg, the rest of that part of the leg and the fore leg and the foot are 

 regenerated. The new part is at first smaller than the part removed, 

 although it may contain all the elements characteristic of the leg. It 

 gradually increases in size until it has grown to the same size as the 

 leg on the other side of the body, and then its growth comes to an 

 end. 



Other parts of the body of the salamander also have the power of 

 regeneration. If a part of the tail is cut off, as much is renewed as 

 has been removed ; if a part of the lower or upper jaw is cut off, the 

 missing part is regenerated ; if a part of the eye is removed, a new eye 

 is formed from the part that remains ; but if the whole eye is extir- 

 pated, or the whole limb, together with the shoulder girdle, is removed, 

 neither structure is regenerated. 



In other vertebrates the power of regeneration is more limited. 

 A lizard can regenerate its tail, but not its limbs. A dog can regen- 

 erate neither its limbs nor its tail. 



It has been stated that the new limb of the salamander is at first 

 smaller than the one removed, but it may contain all the elements of 

 the original limb. We find this same phenomenon in other forms, 

 and since it is a point of some theoretical interest, a few other 

 examples may be given. If the tail of a fish that has a bilobed form 

 is cut off near the base, as indicated in Fig. 40, G, there appears over 

 the exposed edge a narrow band of new material. The new part 



