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SCIENCE. 



[N. S. Vol. XIV. No. 346. 



however, even in these forms that when the 

 leg is cut off at the coxa it regenerates bet- 

 ter than when cut off at any other level. 

 Schultz adds that we see here an excellent 

 example of how regeneration is influenced 

 by natural selection, since regeneration 

 takes place best where the leg is most 

 often broken off. On the other hand, the 

 author hastens to add that since regen- 

 eration also takes place when the leg is 

 cut off at any other level this shows that 

 the power to regenerate is characteristic of 

 all parts of the organism, and is not only a 

 phenomenon of adaptation, as Weismann 

 believes. It seems highly improbable that 

 a spider could ever lose a leg in the middle 

 of a segment, i. e., between two joints, since 

 the segments are hard and strong, and the 

 joints much weaker, but nevertheless the 

 leg has the power to regenerate also from 

 the middle of the segment, if cut off in this 

 region. 



The formation of the new part takes place 

 somewhat differently, according to Schultz, 

 when the leg is amputated between two seg- 

 ments than when cut off at the coxa. In the 

 latter case, there is produced from the cut 

 end of the last segment a solid rod which, 

 as it grows longer, bends on itself several 

 times. Joints appear in the rod, beginning 

 at the base. The leg is set free at the next 

 moult. If the leg is cut off nearer the distal 

 end a smaller rod is formed, that extends 

 straight forward, or may be thrown into a 

 series of folds. It lies, however, inside of 

 the last segment, since the surface exposed 

 by the cut is quickly covered over by a 

 chitinous covering. The piece is set free 

 at the next moult. 



Loeb has found that if the body of the 

 pycnogonid, Phoxichilidium maxillare, is cut 

 in two there regenerates from the posterior 

 end of the anterior half a new body-like 

 outgrowth. 



Without attempting to describe the many 

 cases in worms and molluscs in which there 



is no obvious connection between the power 

 of the part to regenerate and its liability to 

 injury, but where it is more difficult to show 

 that it may not exist, let us pass to an ex- 

 amination of the regeneration of the starfish. 

 It has been known since the time of Reau- 

 mur that starfish have the power of regen- 

 erating new arms if the old ones are lost. 

 It has been claimed that in certain starfishes 

 an arm itself can produce a new starfish 

 (Haeckel (78), P. and E. Sarasin ('88), 

 von Martens ('84) and Sars ('75)), but 

 this has been denied by other observers. It 

 has not been found to take place in several 

 species of starfishes, but if a portion — even 

 a small piece — of the disc is left with the 

 arm a new disc and arms may develop 

 (Fig. 38, F). When the arm of Asterias 

 vulgaris is injured it pinches off in many 

 cases at its base, and a new arm grows 

 out from the short stump that remains. 

 These same starfishes that are regener- 

 ating new arms in their natural envi- 

 ronment have the new arms almost al- 

 ways arising from this breaking region.* 

 Thus King found out of 1914 individ- 

 uals of Asterias vulgaris collected at ran- 

 dom, 206, or 10.7 per cent., had one or 

 more new arms, and all these except one 

 arose from near the disc. In other species 

 it appears that the outer portions of the 

 arm may be broken off without the rest of 

 the arm being thrown off. King has found 

 that in asterias, regeneration takes place 



* The Sarasins have described several cases in Linkia 

 multiformis in vphich an old arm has one or more new 

 arms arising from it. In one case, copied in our Fig. 

 38, G, four rays arise from the end of one arm, pro- 

 ducing the appearance of a new starfish. In fact the 

 Sarasins interpret the result in this way, although 

 they state that there is no madreporite on the upper 

 surface, and they did not determine whether a 

 mouth is formed at the convergence of the rays, 

 because they did not wish to destroy so unique 

 a specimen — even to find out the meaning of it. 

 There seems to me little probability that the new 

 structure is a starfish, but the old arm has been so 

 injured that it has produced a number of new arms. 



