July 29, 1904.] 



SCIENCE. 



151 



ciple of variation must be a far more important 

 factor in tlie result than the picking out of the 

 most extreme variations. The same laws that 

 determine that one individual varies in a useful 

 direction farther than do other individuals may, 

 after all, account for the entire series of changes. 

 If it be replied that natural selection does not 

 take into account the causes of the differences of 

 individual varia,tion, this is to admit that it 

 avowedly leaves out of account the very prin- 

 ciples that may in themselves, and without the 

 aid of any such supposed process as natural selec- 

 tion, bring about the result. The Lamarckian 

 principle of use and disuse does not give an ex- 

 planation of autotomy, since the region of tha 

 breaking-joint is not the weakest region of the 

 leg, or the place at which the leg would be most 

 likely to be injured. 



We can not assume autotomy to be a fvinda- 

 mental character of living things, since it occurs 

 only under special conditions, and in special 

 regions of the body. While it might be possible 

 to trace the autotomy of the legs of the Crustacea, 

 myriapods and insects, to a common ancestral 

 form, yet this is extremely improbable, because 

 the process takes place in only a relatively few 

 forms in each group. The autotomy of the wings 

 of white ants that takes place along a preexisting 

 breaking line must certainly have been independ- 

 ently acquired in this group. The breaking off of 

 the end of the foot in the snail helicarion is also 

 a special acquirement within the group of mol- 

 lusca. 



Bordage has suggested that the development of 

 the breaking joint at the base of the leg of 

 phasmids has been acquired in connection with 

 the process of moulting. He lias observed that 

 during this period the leg can not, in some cases, 

 be successfully withdrawn through the small basal 

 region; and hence, if it could not break off, the 

 animal would remain anchored to the old exo- 

 skeleton. It escapes at the expense of losing its 

 leg. The animal, having acquired the means of 

 breaking off its leg under these conditions, might 

 also make use of the same mechanism when the 

 leg is held or injured, and thereby escape its 

 enemy. The fact that the crayfish has a break- 

 ing joint only for the large first pair of legs would 

 seem to be in favor of this interpretation, but the 

 crab has the same mechanism for the slender 

 walking legs that one would suppose could be 

 easily withdrawn from the old covering. It 

 should also be remembered that we do not know 

 whether the breaking joint at the base of the leg 

 of the crab and of the crayfish would act at the 

 time when the leg is being withdrawn from the 



old exoskeleton, unless the leg were first injured 

 outside of the joint. 



Our analysis leads to the conclusion that we 

 can neither account for the phenomenon of 

 autotomy as due . to internal causes alone in 

 the sense of its being a general property of 

 protoplasm, nor to an external cause, in the sense 

 of a reaction to injuiy or loss, from accident. 

 There would seem then only one possibility left, 

 namely, that it is a result of both together, or in 

 other words, a process that the animal has ac- 

 quired in connection with the conditions under 

 which it lives, or in other words, an adaptive re- 

 sponse of the organism to its conditions of life. 



We are not, however, able at present to push 

 these questions farther, for, however probable it 

 may seem that animals and plants may acquire 

 characteristics useful to them in their special 

 conditions of life, and yet not of suificient impor- 

 tance to be decisive in a life-and-death struggle, 

 still we can not, at present, state how this could 

 have taken place in the course of evolution. For, 

 however plausible it may appear that the useful 

 structure has been built up through an inter- 

 action between the organism and its environment, 

 we can not afford to leave out of sight another 

 possibility, viz., that the structure or action may 

 have appeared independently of the environment, 

 but after it appeared the organism adopted a 

 new environment to which its new characters 

 made it better suited. If the latter alternative is 

 true, we should look in vain if we tried to find 

 out how the interaction of the environment 

 brought about the adaptation. The relation 

 would not be a causal one, in a physical sense, 

 but the outcome\ of a different sort of a relation, 

 viz., the restriction of the organism to the environ- 

 ment in which it can remain in existence and leave 

 descendants. 



For one whose life consists of a struggle for 

 existence, it is difficult to appreciate the deli- 

 cate humor with which Professor Morgan ' ad- 

 mits ' natural selection for the sake of argu- 

 ment; it is more difficult for him to under- 

 stand the objection that variations are not 

 fit until they have been fitted into some part 

 of the external world; but it is harder yet for 

 him to see that ' the restriction of the organism 

 to the environment in which it can remain in 

 existence and leave descendants ' differs from 

 ' natural selection ' except in the number of 

 words used to express the same idea. These 

 minor points, however, have little bearing on 

 the evidence from autotomy. To appreciate 



