THEORY OF FERTILIZATION. 



*57 



SUMMARY. 



I. Old theories of "ovists," "animalculists," and of the "aura seminalis." 



II. Modern morphological theories incline to lay the whole emphasis upon 

 the nuclei. The conclusions of Hertwig and Strasburger are strongly in favor ot 

 this view. The claims of the cell-substance and general protoplasm must not, 

 however, be overlooked. Many facts, such as those demonstrated by Boveri, 

 show, that the protopasm is also important. 



III. Modern physiological theories of fertilization are necessarily very 

 tentative. Sachs compares it to fermentation ; Rolph to mutual digestion. To 

 Weismann, the process appears quantitative rather than qualitative, so far as 

 the subsequent division is concerned. Half of the keimplasma which the ovum 

 has surrendered with the second polar globule is restored by the sperm-nucleus. 

 The two nuclei are alike, and thus there is virtually no sex. Protest against 

 this. The male cell brings to the ovum a supply of characteristic katastates. 



IV. Uses of fertilization to the species. Many regard fertilization as a 

 necessary rejuvenescence of the life of the species. Weismann criticises this 

 view, but his criticism must be read in the light of the researches of Maupas, 

 who has shown that without conjugation the members of an isolated family of 

 infusorians eventually cease to feed and divide, passing through stages ot 

 degeneration and senility to extinction. In this case, conjugation is essential to 

 the continued vitality of the species. According to Brooks, fertilization is an 

 important source of variation ; according to Weismann, it is really the sole 

 source. 



LITERATURE. 



Works already cited. 



Hertwig, O. — Das Problem der Befruchtung, &c; Jenaische Zeitschrift fur 



Naturwissenschaften, XVIII., 1885. 

 Maupas, E. — Comptes Rendus, 1886, 1887; and Archives de Zoologie 



experimentale, 1888. 

 Strasburger, E. — Neue Untersuchungen iiber den Befruchtungsvorgang 



bei den Phanerogamen, als Grundlage fiir eine Theorie der Zeugung. 



Jena, 1884. 

 Weismann, A. — Opp. cit., especially Die Bedeutung der sexuellen Fortpflan- 



zung fur die Selektions-Theone. Jena, 1886. 



