18 



REGENERA TION 



Regeneration takes place not only in adult organisms, but also in 

 embryos, and larvae of many animals. It is often stated that the 

 power of regeneration is more highly developed in embryos than in 

 adults, but the facts that can be advanced in support of this view 

 are not numerous. One of the few cases of this sort known to us 

 is that of the leg of the frog, that does not regenerate, while the leg 

 of the tadpole is capable of regenerating. 



B 



FIG. ii. A. Blastula of Sea-urchin. Dotted lines indicate where pieces of wall were cut off. To 

 the right are shown stages in the development of these pieces. B. Two-cell stage of egg 

 of sea-urchin. One blastomere isolated. Its development shown in figures to right of B. 

 C. Fertilized but unsegmented egg. Dotted line indicates where it was cut in two. Upper 

 row of figures to right shows development of nucleated piece ; lower row shows the fertiliza- 

 tion and development of non-nucleated piece. 



The early stages in the development of the sea-urchin, or of the star- 

 fish, may be taken to illustrate the power of regeneration in embryos. 

 If the hollow blastula of the sea-urchin is cut into pieces (Fig. n, A), 

 each piece, if not too small, may produce a new blastula. The 



