306 EMBRYOLOGY 



shown the necessity of a reduction process from purely theoretic 

 considerations. He said: "If, in every propagation by fertilization, 

 the volume of the idioplasm, however constituted, doubles itself, 

 the idioplasm body would be so much increased, after several 

 generations, that it could no longer find room in a spermatozoon. 

 It is thus absolutely necessary that indigenous propagation the union 

 of the parental idioplasm bodies occur without causing, by the united 

 mass, a corresponding increasing growth of this material." 



The process suspected by Naegeli was soon after discovered in 

 the development of the polar cells, which, however, were first ex- 

 plained in another way by their discoverer himself, Ed. van Beneden, 

 and were first recognized by Weismann as the process by which a 

 summation of the parental mass as a result of fertilization was pre- 

 vented. Weismann agrees with Naegeli that reduction was so cer- 

 tainly required by theoretic considerations that the process by which 

 this occurred must be found if it were not contained in already 

 known facts. I, however, doubt as little as does Weismann that 

 the reduction of the idioplasm, which is theoretically demanded, 

 occurs by the formation of polar cells. 



When one fact thus agrees with another, which is very rare in 

 this way in biologic processes, we may certainly say, in spite of the 

 objections raised by several investigators, that the idioplasm of 

 Naegeli is found in the chromatin of the cell-nucleus, and that this 

 hypothesis is adapted in a high degree to serve as a starting-point 

 and leading star. 



How many questions whose solutions in part we are already 

 beginning to determine, which in part wait upon the future, force 

 themselves upon the investigator ! 



Does an actual penetration of the. two idioplasms occur during 

 the union of the egg- and sperm-nuclei, or do they remain alongside 

 of one another, temporarily or permanently ? and in corresponding 

 way, how does the reduction process act? To how many ques- 

 tions, again, the origin of female and male sex and the generation 

 of bastards gives rise! May we find a morphological basis by the 

 study of the sexual production of bastards for the law of Mendel, 

 which has been confirmed in great part by recent investigations of 

 Tschermak, Correnz, and De Vries on bastards ? 



And what a perspective the following consideration opens! If 

 the chromatin is the substance by which the peculiarity of each 

 organism is determined, it must be of somewhat different composi- 

 tion in each of the numberless organized species. In the insigni- 

 ficant mass of an egg-nucleus, or a sperm-nucleus in the head of 

 a spermatozoon, only visible under the microscope, the numberless 

 peculiarities by which one species is separated from another are 

 compressed in their elementary forms. Will human intelligence 



