130 Facts Compelling Us to Reject Preformation 
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.*® 
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 
°8G. Born: Ibid. P. 141. 
°°G. Born: Ibid. P. 69—86. 
