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SCIENCE 



[N. S. Vol. XXXVII. No. 961 



binations established by the entrance into 

 the eggs of spermatozoa with or without 

 the X-ehromosome persist throughout the 

 whole development of the individual until 

 new germ-eells are formed. 



A second fundamentally important ques- 

 tion, concerning which no general consen- 

 sus of cytologists has yet been reached, 

 relates to the mode of union of the chromo- 

 somes in synapsis and the subsequent dis- 

 tribution of their substance to the germ- 

 cells. Only in a few special cases has com- 

 plete proof been attained of a conjugation 

 followed by complete disjunction or sepa- 

 ration of the original conjugating chromo- 

 somes. Until this complicated and difficult 

 problem has been much more thoroughly 

 studied we shall not be in a position to ex- 

 plain exactly what is the mechanism of 

 Mendel's law of heredity and the distribu- 

 tion of the unit-factors to the germ-cells. 

 We are not dealing with a closed chapter 

 in the study of heredity. Both genetic and 

 microscopical research are still in a forma- 

 tive stage. It is hardly a decade since they 

 finally converged upon the same specific 

 problems. We must not yet make too ex- 

 acting a demand upon the explanatory ca- 

 pacity of either ; and it is a part of the pres- 

 ent interest of the subject that so much still 

 remains to be accomplished. 



We have thus arrived at some of the 

 most advanced and difficult questions in 

 this field of inquiry. Perhaps I have not 

 succeeded in making entirely clear even 

 the few illustrative eases that have been 

 considered. If so, I must plead in extenu- 

 ation that the subject is beset with tech- 

 nical difficulties ; and we biological folk 

 have come to speak a language that is 

 strange to many of our fellows. But I 

 have been less concerned with the presen- 

 tation of particular results or the critical 

 discussion of details than with the indica- 

 tion of a point of view ; I have only wished 

 to point out one of the pathways along 



which students of cytology are attempting 

 to cooperate with students of genetics in 

 their attack upon the problems of heredity. 

 I would like to urge in closing that such 

 explanations as have here been briefly in- 

 dicated are not mere vague and general 

 notions. They are specific and detailed 

 interpretations of observed facts. They 

 enable us, up to a certain point, to com- 

 prehend what goes on in the germ-cells, 

 to form perfectly clear mental pictures 

 of the apparatus of heredity, and of its 

 mode of action in particular cases. They 

 contain no mystical or transcendental ele- 

 ment. I repeat that they are entirely in 

 accord with the principles of chemical 

 physiology, and with the experimental 

 results upon the physiology of develop- 

 ment. To this extent at least the explana- 

 tions are real and represent a partial solu- 

 tion of the problem of heredity. No one 

 would maintain that these explanations 

 are final. I do not doubt that with 

 advancing knowledge we shall in time 

 come to look back upon many of our 

 present conceptions as crude and naive. 

 Discovery in this great field of research has 

 made no approach to its limit. Great 

 progress in the future is certain. But if 

 you ask whether we may hope to reach at 

 last a complete or final solution of the 

 problem of heredity, I fear the answer 

 must be, no. The man of science should 

 be the first to admit that science can not 

 attain to a complete understanding of any- 

 thing. The explanation of any phenom- 

 enon only uncovers new phenomena behind 

 it that still demand explanation, in endless 

 succession ; and such is the essential char- 

 acteristic of scientific progress. Science 

 does not aim at ultimate explanations ; and 

 could we find them, science would be 

 emptied of its interest to the investigator. 

 Edmund B. Wilson 

 Columbia U'Jiversitt 



