LITEEATURE. 47 



nucleus ; in many objects they remain for a considerable time near 

 each other, but not united, and only later are together metamorphosed 

 into the segmentation-spindle. 



9. In some animals fertilisation of the egg takes place only after 

 completion of its maturation, but in others it is inaugurated at the 

 very beginning of maturation, so that the two phenomena overlap 

 each other. 



10. Fertilisation theory. Fertilisation depends on the copulation 

 of two cell-nuclei, which are derived from a male cell and a female 

 cell. 



11. Theory of heredity. The male and female nuclear substances 

 contained in the spermatic nucleus and the egg-nucleus are the 

 bearers of the peculiarities which are transmissible from parents to 

 their offspring. 



LITERATURE. 



Agassiz and Whitman. The Development of Osseous Fishes. II. The 

 pre-embryonic Stages of Development. Pt. 2. The History of the Egg 

 from Fertilization to Cleavage. Mem. Museum Comp. Zoology at Harvard 

 College. Vol. XIV. No. I. Part II. 1889. 



Balfour. On the Phenomena accompanying the Maturation and Im- 

 pregnation of the Ovum. Quart. Jour. Micr. Sci. Vol. XVIII. 1878, 

 p. 109. 



Bambeke. Recherches sur 1'Embryologie des Batraciens. Bull, de 1'Acad. 

 roy. Sci. de Belgique. 2me se>. T. LXI. 1876. 



Beneden, Ed. van, et Charles Julin. Observations sur la maturation, la 

 fecondation et la segmentation de 1'oeuf chez les cheiropteres. Archives 

 de Biologic. T. I. 1880, p. 551. 



Beneden, E. van. La maturation de 1'oeuf, la fecondation, etc., des mammi- 

 feres. Bull, de 1'Acad. roy. Sci. de Belgique. 2me ser. T. XL. Nr. 12. 

 1875. 



Beneden, E. van. Contributions a 1'histoire de la vesicule germinative, etc. 

 Bull, de 1'Acad. roy. Sci. de Belgique. 2me ser. T. XLI. Nr. 1. 1876. 



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

 la division cellulaire. Archives de Biologic. T. IV. Paris 1883. 



jBeneden, van, et Neyt. Nouvelles recherohes sur la fecondation et la 

 division mitosique chez 1'Ascaride megalocephale. Leipzig 1887. And 

 Bull, de 1'Acad. roy. Sci. de Belgique. 3me ser. T. XIV. p. 215. 



Blochmann. Ueber die Eichtungskorper bei den Insecteneiern. Biol. Cen- 

 tralblatt. Bd. VII. 1887. 



Blochmann. Ueber die Richtungskorper bei Insecteneiern. MorphoL Jahrb 

 Bd. XII. 1887, p. 544. 



Blochmann. Ueber die Reifung der Eier bei Ameisen und Wespen. Fest- 

 schrift zur Feier des 500jiihr. Bestehens der Univ. Heidelberg. 1886. 

 Med. Theil. 



