244 THE PROTOZOA 



sexual activity. The egg is a potential individual as shown by the 

 facts of parthenogenesis, where, without fertilization, the egg develops 

 to form a new individual. The first appearance of this individual 

 goes back to the germ-glands, where it results from the division of an 

 oogonium. Here is the reproductive act proper ; fertilization is only 

 the liberation of an inhibited development through which the poten- 

 tial individual becomes actual. It leads to no increase, but rather to 

 decrease of individuals, since two potential individuals egg-cell and 

 sperm-cell join to form one body." 1 



The phrase "liberation of an inhibited development," if applied to 

 the effect of conjugation among the Protozoa, might be translated into 

 Biitschli's " Verjiingung" ('76), or Engelmann's "Reorganization" 

 ('76), or Maupas's " Rejeunissement." In no case does word or 

 phrase explain the phenomenon. From all the facts known at the 

 present time, the only conclusion that can be drawn is that conjuga- 

 tion, apparently, is not the cause of reproduction, but as Biitschli, 

 Engelmann, and Minot long since pointed out, in some unknown 

 way provides the energy for continuing the functions of the indi- 

 vidual, including the power of reproducing. 



SPECIAL BIBLIOGRAPHY VII 



Biitschli, 0. Studien liber die ersten Entwicklungsvorgange der Eizelle, der Zell- 



theilung und die Conjugation der Infusorien. Abh. d. Senckenb. naturf. Gesell. 



Frankfurt a. Main, X., pp. 213-452, 1876. 

 Engelmann, Th. W. Ueber Entwickelung und Fortpflanzung von Infusorien. 



Morphol. Jahrb., pp. 573-635, 1876. 



Geddes and Thompson. The Evolution of Sex. London, 1889. 

 Hartog, M. M. Some Problems of Reproduction, etc. Q. J. M. S., XXXIII., 



pp. 1-81, 1891. 

 Hertwig, R. Ueber Kerntheilung, Richtungskbrperbildung und Befruchtung von 



Actinosphasrium Eich. Abh. d. K. bay. Akad. d. Wiss. Miinchen, 11. Kl. 



XIX., 1898. 

 Hertwig, R. Mit welchem Recht unterscheidet man geschlechtliche und unge- 



schlechtliche Fortpflanzung ? Sitz. Ber. d. Ges.f. Morph. u. Physiol. Munchen, 



II., 1899. 

 Maupas. M. Le re"jeunissement karyogamique chez les cilies. Arch. d. zool. exper. 



et gene"r., (2) VII., pp. 149-517, 1889. 



Minot, C. S. Growth as a Function of Cells. Proc. Bost. Soc. Nat. Hist., XX., 1879. 

 Schaudinn, F. Ueber den Zeugungkreis von Paramreba Eilhardi. Sitz. Ber. Akad. 



Wiss. Berlin, 1896. 

 Siedlecki, M. Ueber die geschlechtliche Vermehrung der Monocystis ascidiae 



R. Lan. Bull. d. rAcad. d. Sci. d. Cracovie, December, 1899. 

 Wilson, E. B. The Cell in Development and Inheritance. 2d ed. New York, 



1900. 



1 loc. cit., p. 97. 



