IOWA ACADEMY OF SCIENCES. 



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sive generation to resemble, not the adult of the preceding, 

 but earl}^ stages of the immature organism. It is an estab- 

 lished fact that new characters appear in most cases at or 

 towards the close of individual development, but as off- 

 spring are largely produced before this time, it is an abso- 

 lute impossibility that gemmules should pass into the 

 hereditary substance from the organs of the parent in 

 their modified state. 



When we try to discover the time at which the predom- 

 inant mass of gemmules is given off from the various 

 organs, we find the above objection becoming even more 

 important than it at first seemed. If in an animal at a very 

 early stage of development, certain organs are entirely 

 removed, rendering it impossible for those organs to give 

 oft* gemmules, nevertheless such organs are produced in the 

 offspring of the next generation as if there had been no 

 mutilation in the parent. 



Another general objection is based on the inconceiva- 

 bility of the gemmules reaching their proper locations in 

 the germinal substance built up from them, and unless 

 we assume that they do reach a definite location and thus 

 build up a definite structure, it is inconceivable that the 

 various parts of the adult arising from their development 

 should have the proper relations one to another. 



A large share of the objections to the theory, although 

 when taken as a whole, they are the most important of all, 

 cannot be entered into here as they would lead us into a 

 discussion of masses of details of structure and develop- 

 ment not suited to a paper of this kind. It may be stated, 

 liowever, that these are on the whole so forcible that biol- 

 ogists in general have been compelled to abandon the 

 theory of pangenesis as untenable. 



Another hypothesis of the origin of the germ, entirely 

 opposed to that of pangenesis and related theories, is that 

 which has come to be known under Weismann's name, 

 the continuity of the germ plasm. This biologist, although 

 not the first propounder of the main idea which gives a 

 name to this theory, has so elaborated the original funda- 

 mental hypothesis that it is usually connected with his 



