THE LIFE CYCLE 



355 



body — a division that, as every one knows, would be in- 

 stantly fatal to any of the higher animals. Most arthropods 

 regenerate lost appendages readily, but slowly, the new 

 appendage increasing in size a little at every moult. The 

 crawfish (and many of its allies) is so provided against the 

 loss of its legs that a special breaking place is developed 

 across the middle of the second joint in them, a groove across 

 the joint, and folds of membranes wdthin it, that prevent 



T 



g\j' 



Fig. 205. Regeneration in Planaria (a to g after Morgan; h, 

 after Voigt). a, a planaria that was divided as indicated 

 along the median line of the body, b, c, d, the regeneration 

 of the left half, that was fed. e, f, g, the regeneration of the 

 other half that had no food, h, regeneration of pieces 

 obliquely cleft partly free from the body: at x a new tail 

 and at y a new head and at z both a new tail and a new head 

 have appeared. 



excess of bleeding when the leg breaks off. Specimens are 

 collected not infrequently, having one of the big claws 

 much smaller than the other, and in process of regeneration; 

 a crawfish, seized by one of the big claws will sometimes 

 automatically cast it off and escape without it. Indeed, 

 so readily are the big claws of the related fiddler crabs cast 

 off, that in handling the crabs one may hardly touch the 

 claws without inviting their loss. 



