August 16, 1901.] 



SCIENCE. 



239 



let us rather attempt to get at a general idea 

 of Weismann's views. In a later paper 

 (1900), in reply to certain criticisms, lie has 

 stated his position somewhat more lucidly. 

 In the following statement I have tried to 

 give the essential part of his hypotheses: 

 Weismann believes the process of regenera- 

 tion to be regulated by ' natural selection '; in 

 fact, he states that it has arisen through such 

 a process in the lower animals — since they are 

 more subject to injury — and that it has been 

 lost in the higher forms except where, on ac- 

 count of injury, it has been retained in cer- 

 tain parts. Thus when Weismann speaks of 

 regeneration as being an adaptation of the 

 organism to its environment, we must under- 

 stand him to mean that this adaptation is 

 the result of the action of natural selection. 

 We should be on our guard not to be misled 

 by the statement that because regeneration 

 is useful to the animal, it has been acquired 

 by natural selection, since it is possible 

 that regeneration might be more or less use- 

 ful without in any way involving the idea 

 that natural selection is the originator of 

 this or of any other adaptation. It will be 

 seen, therefore, that in order to meet Weis- 

 mann on his own ground it will be neces- 

 sary to have a clear understanding in re- 

 gard to the relation of regeneration to 

 Darwin's principle of natural selection. 

 With Weismann's special hypothesis of the 

 'mechanism,' so-called, by which regener- 

 ation is made possible we have here nothing 

 to do, but may consider it on its own merits 

 in another chapter. 



In order to have before us the material 

 for a discussion of the possible influence of 

 natural selection on regeneration, let us first 

 examine the facts that bear on the question 

 of the liability of the parts to injury and 

 their power to regenerate, and in this con- 

 nection the questions concerning the re- 

 newal of parts that are thrown ofl" by the 

 animals themselves in response to an exter- 

 nal stimulus are worthy of careful consid- 



eration. A comparison between the regen- 

 eration of these parts with that of other 

 parts of the same animal gives also impor- 

 tant data. Furthermore, a comparison may 

 be made between different parts of the same 

 animal, or between the same parts of dif- 

 ferent animals living under similar or under 

 dissimilar conditions. 



There are only a few cases known in 

 which a systematic examination has been 

 carried out of the power of regeneration of 

 the different parts of the body of the same 

 animal. Spallanzani's results show that 

 those salamanders that can regenerate their 

 forelegs can regenerate their hind legs also. 

 Towle, who has examined in my laboratory 

 the regeneration of a number of American 

 newts and salamanders, finds also that both 

 the fore and hind legs regenerate in the 

 same forms. The tail and the gills, in 

 those newts with external gills, also regen- 

 erate. It has also been shown in triton 

 that the eye regenerates if a portion of the 

 bulb is left. Broussonet first showed (1786) 

 that the fins of fish have the power to re- 

 generate, although, strangely enough, 

 Fraisse and Weismann state that very little 

 power of regeneration is present in the fins 

 of fish. I have found that the fins of sev- 

 eral kinds of fish regenerate, belonging to 

 widely difierent families.* In Fundulus 

 heteroditus I have found that the pectoral, 

 pelvic, caudal, anal, and dorsal fins have 

 the power of regeneration. In reptiles the 

 feet do not regenerate, at least no cases 

 are known, but the tail of lizards has this 

 power well developed. In birds neither the 

 wings nor the feet regenerate, but Fraisse 

 has recorded the case of a stork in which, 

 the lower jaw being broken ofi", and the 

 upper being cut off at the same level, both 

 regenerated. Bordage has recorded the re- 



* Fundulus heteroditus, Stenopus chrysops, Decap- 

 terus macrella, Menticirrhus macrella, Carassius aura- 

 tus, Phoxinus funduloides, Noturus sp., and a few 

 others. 



