SUMMARY AND CONCLUSION I/I 



more than this, the germ-cells come to differ in their morphological 

 composition ; for in plants the male germ-cell loses its plastids, 

 which are supplied by the mother alone, while in most if not all 

 animals the egg loses its centrosome, which is then supplied by the 

 father. The loss of the centrosome by the egg is, I believe, to be 

 regarded as a provision to guard against parthenogenesis and to 

 ensure amphimixis. 



Tke equivalence of the germ-cells is thus finally lost. Only the 

 germ-nuclei retain their primitive morphological equivalence. Hence 

 zve find the essential fact of fertilization and sexual reproduction to 

 be a union of equivalent nuclei; and to this all other processes are 

 tributary. The substance of the germ-nuclei, giving rise to the 

 same number of chromosomes in each, is equally distributed to the 

 daughter-cells and probably to all the cells of the body. 



As regards the most highly differentiated type of fertilization and 

 development we thus reach the following conception : From the 

 mother comes in the main the cytoplasm of the embryonic body 

 which is the principal substratum of growth and differentiation. 

 From both parents comes the hereditary basis or chromatin by which 

 these processes are controlled and from which they receive the spe- 

 cific stamp of the race. From the father comes the centrosome to 

 organize the machinery of mitotic division by which the egg splits up 

 into the elements of the tissues, and by which each of these elements 

 receives its quota of the common heritage of chromatin. Huxley hit 

 the mark two score years ago when in the words that head this chap- 

 ter he compared the organism to a web of which the warp is derived 

 from the female and woof from the male. What has since been 

 gained is the knowledge that this web is to be sought in the chro- 

 matic substance of the nuclei, and that the centrosome is the weaver 

 at the loom. 



LITERATURE IV 



Van Beneden, E. Recherches sur la maturation de 1'oeuf, la fecondation et la division 



cellulaire: Arch. Biol., IV. 1883. 

 Van Beneden and Neyt. Nouvelles recherches sur la fecondation et la division 



mitosique chez 1'Ascaride megalocephale : Bull. Acad. roy. de Belgique, III. 14, 



No. 8, 1887. 

 Boveri, Th. Uber den Anteil des Spermatozoon an der Teilung des Eies : Sitz.- 



Ber. d. Ges.f. Morph. u. Phys. in Munchen, B. III., Heft 3. 1887. 

 Id. Zellenstudien, II. 1888. 



Id. Befruchtung : Merkel und Bonnet's Ergebnisse, I. 1891 . 

 Id. Uber das Verhalten der Centrosomen bei der Befruchtung des Seeigeleies, 



etc.: VerhandL Phys. Med. Ges. Wurzbitrg, XXIX. 1895. 

 Fick, R. Uber die Reifung und Befruchtung des Axolotleies : Zeitschr. Wiss. 



Zool., LVI. 4. 1893. 



