GEXERAL OUTLINE 1 83 



ing the meaning of the polar bodies had been put forward.^ His 

 interpretation was based on a remarkable paper published by Wil- 

 helm Roux in 1883,^ in which are developed certain ideas which 

 afterwards formed the foundation of Weismann's whole theory of in- 

 heritance and development. Roux argued that the facts of mitosis 

 are only explicable under the assumption that chromatin is not a 

 uniform and homogeneous substance, but differs qualitatively in differ- 

 ent regions of the nucleus ; that the collection of the chromatin into a 

 thread and its accurate division into two halves is meaningless unless 

 the chromatin in different regions of the thread represents different 

 qualities which are to be divided and distributed to the daughter- 

 cells according to some definite law. He urged that if the chromatin 

 were qualitatively the same throughout the nucleus, direct division 

 would be as efficacious as indirect, and the complicated apparatus of 

 mitosis would be superfluous. Roux and Weismann, each in his own 

 way, subsequently elaborated this conception to a complete theory of 

 inheritance and development, but at this point we may confine our 

 attention to the views of Weismann. The starting-point of his theory 

 is the hypothesis of De Vries that the chromatin is a congeries or 

 colony of invisible self- propagating vital units or biopJiorcs somewhat 

 like Darwin's " gemmules " (p. 303), each of which has the power of 

 determining the development of a particular quality. Weismann 

 conceives these units as aggregated to form units of a higher 

 order known as " determinants," which in turn are grouped to form 



^ Of these we need only consider at this point the very interesting suggestion of Minot 

 ('77), afterwards 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 constituents, 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 fertiliza- 

 tion 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 

 A'an 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 quali- 

 ties are transmitted by the egg-cell, while the sperm-cell also transmits female qualities. 

 The germ-cells are therefore non-sexual; they are physiologically as well as morphologi- 

 cally equivalent. The researches of Hertwig, Brauer, and Boveri show, moreover, that in 

 Ascaris, at any rate, all of the four spermatids derived from a spermatocyte become func- 

 tional spermatozoa, and the beautiful parallel between spermatogenesis and oogenesis thus 

 established becomes meaningless under Minot's view. This hypothesis must, therefore, in 

 my opinion, be abandoned. 



Balfour probably stated the exact 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." 



^ tJber die Bedeutung der Kerntheilungsfiguren. 



