GRAFTING AND REGENERATION 



171 



formed, and no subsequent regeneration takes place (Fig. 52, A). 

 Long worms can be made by uniting two pieces, each more than half 

 the length of a worm, or by uniting three pieces, as shown in Fig. 52, C. 

 Short worms can be formed by cutting a middle piece from a worm, 

 and uniting the anterior and posterior pieces (Fig. 53, D). Joest 

 found that when a short worm is made in this way, so that no repro- 

 ductive region is present, the new worm does not produce new repro- 

 ductive organs. It is conceivable that new reproductive organs might 



FIG. 52. After Joest. A. Union of two pieces of Allolobophora terrestris in normal position. 

 Twenty-two months after operation. B. Union of two pieces Lumbricus rubellus. Pieces 

 turned 180 with respect to each other. C. Union of three pieces of A. terrestris to make a 

 " long worm." D. Union of two worms (by anterior ends) from each of which eight an- 

 terior segments had been removed. After three months. Regenerating two new heads. 

 . A small piece of Lumbricus rubellus grafted upon Allolobophora teirestris. Former re- 

 generated an anterior end. 



have been produced either in the old segments, or by the formation 

 of a new reproductive region between the two united pieces, but 

 neither process takes place. In the long worms two sets of repro- 

 ductive organs, etc., are present. This sort of union is, however, 

 less permanent, as the worms often pull apart. 



Joest also united two posterior ends by their anterior surfaces. 

 In many cases no regeneration took place, and, in the absence of a 

 head, the combination is destined to die, although it may remain 

 alive, without food, for several months. When two very long pieces 



