GRAFTING AND REGENERATION 183 



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Born found that if the anterior half of one tadpole was united to the 

 posterior half of the same or of another tadpole a single individual was 

 formed which he kept alive in several cases until the time of metamor- 

 phosis. If the head of a tadpole is cut off and grafted upon the side 

 of the body of another tadpole, the head will remain alive and con- 

 tinue to develop in its new position, and, if well nourished by means 

 of the connecting blood vessels that develop, it may grow to be as 

 large as the head of the tadpole to which it is attached. Similarly, if 

 the tail of one tadpole is grafted upon the side of the body of another 

 tadpole, it also continues to develop, and at the time of metamorphosis, 

 when the normal tail is absorbed, the additional or misplaced tail also 

 shows signs of breaking down. Even the posterior half of one tad- 

 pole, if grafted to the ventral side of another, may continue to develop, 

 producing legs, etc. 



Born succeeded in uniting tadpoles of different species in several 

 different ways. They were united by their heads or by their ventral 

 surfaces, or longer and shorter tadpoles made by using pieces longer 

 or shorter than a half. In all of these cases there is no regeneration 

 at the place of union, and the internal organ, the digestive tract, ner- 

 vous system, and blood vessels unite when brought into contact. 

 When pieces are united end to end, like organs unite to like, the 

 nerve-cord with the nerve-cord, digestive tract with digestive tract,, 

 segmental duct with segmental duct, coelom with coelom, and although 

 less often, the notochords sometimes join together. The lack of 

 union of the ends of the notochord is explained by its frequent par- 

 tial displacement at the cut-end, for when the cut is made the noto- 

 chord, being tougher than the other structures, is often dragged put of 

 place in one or in both pieces, so that the ends do not meet when the 

 pieces are put together. When like organs are brought together the 

 substance of one unites directly with the substance of the other, and 

 if the organ is a hollow one, as is the digestive tract or the nerve-cord, 

 their cavities also become continuous. There is also, Born states, 

 some evidence to show that if similar organs are not brought exactly 

 in contact their ends find each other and unite, and if they do not at 

 first meet squarely they may do so later. When the ends of unlike 

 organs are brought in contact, as, for instance, the nerve-cord and 

 notochord, they do not unite, but connective tissue develops between 

 them. The union of like parts, Born suggests, may be due to some 

 sort of cytotropism, the outcome of a mutual attraction between simi- 

 lar cells like that which Roux has observed between the isolated 

 cells of the segmented egg of the frog. Born thinks that the first 

 rapid union of the pieces is due to the attraction of the ectoderm of 

 one component for that of the other. 



Born succeeded also in uniting pieces of the tadpoles of different 



