130 Facts Compelling Us to Reject Pre formation 



another." In such cases, which are repeated over and 

 over, there is no escape from the admission that with 

 the progress of growth there has taken place in the 

 blended organs a sort of smoothing out, "Ausglattung," 

 of the external and internal walls, and perhaps even a 

 transitory modification of the normal form, caused simply 

 by the influence of the similar organs growing together. 98 



In other cases there is more than a simple smoothing 

 out of the two surfaces which would not fit together 

 at first. Thus in the union of two parts of the intestine 

 of double monsters, thoracopagi, gastropagi, and ventro- 

 pagi, obtained by cutting off from each of two tadpoles 

 a thin layer of the abdomen, and superimposing the two 

 cut surfaces as usual, there results an exact conjunction 

 of the two thin-walled intestinal tubes in such a man- 

 ner as to constitute a single tube without any trace of 

 the junction which was made. So exact a coaptation 

 can certainly not be effected by the simple superposition 

 of the two tadpoles." 



Sometimes the corresponding organs of the two 

 larvae seem as though seeking each other and reaching 

 out to each other. They both deviate from their ordinary 

 direction in order to be able to unite and extend one 

 into the other. This phenomenon appears character- 

 istically in the fusion of the two vascular systems as is 

 demonstrated in the clearest manner by certain experi- 

 ments in grafting definite portions of tadpoles upon 

 complete tadpoles: as for example, the grafting of the 

 posterior heartless portion of a tadpole upon the abdomen 

 of another complete tadpole : the fusion of the two vas- 

 cular systems is so complete that a single blood circulation 



M G. Born: Ibid. P. 141. 

 "G. Born : Ibid. P. 6986. 



