344 cook 



This fact has bearing upon the conception of heredity, for it 

 takes us another step away from the older idea of a mechanism 

 in the cell, and shows us that the intracellular organs, which 

 some look upon as the mechanisms of heredity, are capable of 

 change and adaptation like other parts of organisms, and that 

 the problem of evolution is not to be solved by the supposition 

 that evolution is determined in advance by mechanisms of 

 heredity. 



In the lower groups the union of the gametes is completed 

 before vegetative growth is resumed, or before the new genera- 

 tion begins. But in the remote ancestors of the higher groups 

 this procedure was abandoned, and the completion of conjuga- 

 tion was deferred. Vegetative growth began to be carried on 

 while the cells were still in the double, conjugating condition. 

 If the form of the adult were strictly predetermined by the inter- 

 nal organs of the cell, the double-celled organisms could have 

 existed only as monstrous doubles of the simple-celled organ- 

 isms which are built up after conjugation is completed. But, 

 as a matter of fact, the structures which were built up from these 

 double, conjugating cells proved to be entirely different from 

 those which had been built previously from simple cells. New 

 evolutions began on entirely independent lines, without refer- 

 ence to the character-units or other equipment of heredity 

 resident in the cells of which the new structures were built. 

 Moreover, the old form of heredity continued to be transmitted, 

 even after new and higher types of organic structures had been 

 intercalated into the life-history of the primitive organism. 



All the liverworts, mosses and ferns continue to build up the 

 two different kinds of cellular structures, one during conjuga- 

 tion and the other after or between conjugations. The two 

 kinds of heredity, the conjugate and the post-conjugate, continue 

 to run peaceably along the same lines of descent, like multiple 

 telegraphic messages on the same wire. 



Such complications do not, of course, dismay the inventors 

 of hereditary mechanisms. Difficulty only adds zest to their 

 ingenuity. Having invented one set of determinants, it is easy 

 to invent another and have them working by turns, as Weis- 

 mann gravely proposed in explaining the alternative heredity of 



