102 RE GENERA TION 



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 pro- 

 duced 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, Pkoxichili- 

 dium 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 

 mollusks 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 examina- 

 tion of the regeneration of the starfish. It has been known since the 

 time of Reaumur that starfish have the power of regenerating new 

 arms if the old ones are lost. It has been stated that in certain 

 starfishes an arm itself can produce a new starfish, Haeckel ('78), 

 P. and R. Sarasin ('88), von Martens ('84), and Sars ('75, but this 

 has been denied by other observers. In several species of starfishes, 

 the separated arm does not regenerate ; but if a portion, even a small 

 piece, of the disk is left with the arm, a new disk and arms may 

 develop (Fig. 38, F). When the arm of Asterias vnlgaris is injured 

 it pinches off in many cases at its base, and a new arm grows out from 

 the short stump that remains. When these starfishes regenerate 

 new arms in their natural environment, the new arms almost always 

 arise from this breaking region. 1 Thus King found out of 1914 

 individuals of Asterias vulgaris collected at random, 206, or 10.7 

 per cent, had one or more new arms, and all these except one arose 

 from near the disk. In other species it appears that the outer por- 

 tions of the arm may be broken off without the rest of the arm being 



1 The Sarasins have described several cases in Linckia multiformis in which 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, producing 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. 



