THE WONDER OF LIFE 569 



an antenna ; in place of an antenna a leg. Instead of a 

 lost abdominal limb the edible crab may grow a walking 

 leg, which is very much out of place, and instead of a lost 

 stalked-eye the lobster may grow an antenna. Many cases, 

 indeed, are known where a Crustacean does not get an eye 

 for an eye, but something simpler. Most of these cases 

 of imperfect regeneration concern animals whose limbs 

 normally pass from one form to another with successive 

 moultings, and, as Przibram suggests, it is worth asking 

 whether the antenna instead of an eye was really the final 

 result of the regenerative process. The animals should be 

 kept alive when possible, and the observation continued 

 until after the next moult. In his experiments on the 

 common water-flea, Daphnia, and on the Isopod, Asellus, 

 he found that the regenerated limb was not at first perfect, 

 but became normal after repeated moultings. 



Regeneration and Embryonic Development. In 

 many cases the process by which regeneration is effected 

 is very like the normal process of typical development, 

 which is perhaps what one should expect on a priori grounds. 

 The ectoderm or outer layer of the cut surface furnishes 

 the ectoderm of the re-growth, and the mesoderm the 

 mesoderm. But in some cases the regenerative growth 

 is very different from that which occurs in embryonic 

 development, and we have to face the puzzle that the same 

 result may be reached by two different paths. 



When the anterior end of a Naiad a freshwater worm 

 is cut off, an ectodermic cap is formed, according to Hepke, 

 over the wound ; in the concave interior of this cap there 

 gradually appear all the organs to be replaced ; muscles, 

 which are normally mesodermic, are formed by cells mig- 

 rating from the ectoderm, and a piece of food- canal, which 



