GENERAL INTRODUCTION 



worms, one of which, at least, seems to have been the annelid lum- 

 briculus. His first experiments (1741) showed that when the worm 

 is cut in two pieces, a new tail develops at the posterior end of the 

 anterior piece, and a new head at the anterior end of the posterior 



j/ 



B 



FIG. i. A-B. After Trembley. C-G'. After Bonnet. A. Seven-headed hydra made by splitting 

 head-ends lengthwise. B. Illustrating the method of turning hydra inside out by means of 

 a bristle: i, foot being pushed through mouth ; 2, completion of process. C. Middle piece 

 of an earthworm (cut into three pieces) with new head and tail. D. Anterior part of an 

 earthworm regenerating a new " delicate " tail. E. Posterior third of a worm (lumbriculus) 

 that regenerated two heads. F. Middle piece of a worm (another species) cut into three 

 pieces. It made a tail at each end. F '. Anterior, enlarged end (tail) of last. G. Small 

 piece of a worm. G'. Regeneration of head and tail of same. 



piece. He found that if a worm is cut into three, four, eight, ten, 

 or even fourteen pieces, each piece produces a new worm ; a new 

 head appearing on the anterior end of each piece, and a new tail on 

 the posterior end (Fig. i, G, G'). The growth of the new head is 

 limited in all cases to the formation of a few segments, but the new 



