GRAFTING 



423 



reproductive organs in the artificially long worms and 

 no reproductive organs at all in the very short worms 

 thus produced. 



Should one endeavor to unite two worms by the ante- 

 rior ends from which the heads have been removed, or 

 by the two posterior ends from which the tails have 

 been cut off, difficulties arise that indicate the strength 

 of the force of polarity among living organisms, for 

 though union may occur, a head often springs by re- 



FIG. 146. Heteroplastic transplantation in the earth-worm, a, Of tail end 

 of another individual of the same species (Allolobophora terrestris) ; b, interca- 

 lation of mid-body region of another individual; c, lateral grafting of another 

 half of another individual. (Joest.) 



generation from the seat of union when anterior, or a 

 tail or a head when posterior, so that the experiment 

 eventuates in the first instance in two worms with a 

 head in common, or in the second, two worms with three 

 heads, or two worms with a tail in common. In posterior 

 sutures the regeneration of the head or tail seems to 

 depend upon the length of the amputated portions. If 

 short, a tail regenerates; if longer, a head or a tail. Mor- 

 gan doubts whether Joest is correct in thinking heads 

 can be regenerated from combined posterior ends. 



