GENERAL OUTLINE 243 



3 . Weismann's Interpretation of Reduction 



Up to this point the facts are clear and intelligible. Before com- 

 ing to closer quarters with them it will be useful to make a digression 

 in order to consider some of the theoretical aspects of reduction ; 

 though the reader must be warned that this will lead us into very 

 uncertain ground traversed by a labyrinth of conflicting hypotheses 

 from which no exit has yet been discovered. 



The process of reduction is very obviously a provision to hold con- 

 stant the number of chromosomes characteristic of the species ; for 

 if it did not occur, the number would be doubled in each succeeding 

 generation through union of the germ-cells. 1 A number of writers 

 have contented themselves with this simple interpretation, Oscar 

 Hertwig, for example, regarding reduction as "merely a process to 

 prevent a summation through fertilization of the nuclear mass and of 

 the chromatic elements." 2 A moment's reflection reveals the entire 

 inadequacy of such an explanation. As far as the chromatin-mass is 

 concerned, it does not agree with the facts ; for in reduction with 

 tetrad-formation the chromatin-mass is reduced not to one-half, but to 

 one-fourth. That reduction must mean more than mere mass-reduc- 

 tion is moreover proved by the fact that the bulk of the nucleus may 

 enormously increase or decrease at different periods in the same cell, 

 irrespective of the number of chromosomes. The real problem is 

 why the number of chromosomes should be held constant. The 



1 Of the many earlier attempts to interpret the meaning of the polar bodies, we need only 

 consider at this point the very interesting suggestion of Minot ('77), afterward adopted by 

 Van Beneden ('83), that the ordinary cell is hermaphrodite, and that maturation is for the 

 purpose of producing a unisexual germ-cell by dividing the mother-cell into its sexual con- 

 stituents, or "genoblasts." Thus, the male element is removed from the egg in the polar 

 bodies, leaving the mature egg a female. In like manner he believed the female element to 

 be cast out during spermatogenesis (in the " Sertoli cells "), thus rendering the spermatozoa 

 male. By the union of the germ-cells in fertilization, the male and female elements are 

 brought together so that the fertilized egg or oosperm is again hermaphrodite or neuter. 

 This ingenious view was independently advocated by Van Beneden in his great work on 

 Ascaris ('83). A fatal objection to it, on which both Strasburger and Weismann have 

 insisted, lies in the fact that male as well as female qualities are transmitted by the egg-cell, 

 while the sperm-cell also transmits female qualities. The germ-cells are therefore non-sexual. 

 The researches of many observers show, moreover, that all of the four spermatids derived 

 from a spermatocyte become functional spermatozoa. Minot's hypothesis must, therefore, in 

 my opinion, be abandoned. 



Balfour doubtless approximated more nearly to the truth when he said, " In the formation 

 of the polar cells part of the constituents of the germinal vesicle, which are requisite for its 

 functions as a complete and independent nucleus, is removed to make room for the supply 

 of the necessary parts to it again by the spermatic nucleus" ('80, p. 62). He fell, however, 

 into the same error as Minot and Van Beneden in characterizing the germ-nuclei as " male " 

 and "female"; and, as shown at pages 194, 353, it has been found that a single germ- 

 nucleus is able to carry out development of an embryo without union with another. 



2 '90, i, p. 112. Cf. Hartog, '91, p. 57. 



