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23 If it could be taken as an absolute certainty that the modifications in the crop resulted originally from changes due to adaptation to new conditions of life and that the skeletal peculiarities have resulted from the alteration in the crop, then a case of this kind would be decisive. For the fact that these characters are now developed in the embryo before there is an opportunity for the modifications to occur through use and disuse of parts, proves that they are no longer produced in each individual independently as a result of functional changes in its own experience and that characters which were originally acquired by the ancestors of those birds have now through inheritance become congenital in the race.

An objection often urged against the belief in the inheritance of acquired characters is that it is difficult to conceive how changes in the soma can affect the reproductive cells in such a way as to bring this result about. But this is no valid argument, for the question can only be settled by an appeal to facts. The microscopical examination of the tissues of plants and animals has during recent years resulted in the discovery of a state of things which tends to remove this difficulty. The cells composing the organisms have in numerous cases been found to have connections with each other by means of protoplasmic threads. This was first of all noted in the sieve tubes of plants, and afterwards the same was found to be true