XII.] CONJUGATION AND SEXUAL REPRODUCTION. 1 89 



egg-cells of a mother would contain identical germ-plasm, if 

 they did not undergo the 'reducing divisions' before reaching 

 maturity,— so all the descendants of an Infusorian after conju- 

 gation would contain similar combinations of idants, if the 

 repeated ' reducing divisions ' did not precede the formation of 

 the reproductive nuclei. 



Variety of individual character in the hereditary substance is thus 

 brought about by means of these divisions. 



The Deeper Significance of Conjugation. 



No one will attempt to oppose the view that the deeper 

 meaning of conjugation is closely connected with that of sexual 

 reproduction. The process is, in both cases, that of nuclear 

 fusion, and, in fact, the formation of a complete nucleus by the 

 union of two 'half-nuclei,' as they may be called, that is, two 

 nuclei which contain only half the normal amount of hereditary 

 substance or idioplasm, and only half the normal number of 

 individual hereditary units or ids. From this fusion a new 

 nucleus is formed which contains that amount of hereditary 

 substance and that number of ids which are normal to the 

 species. This is my explanation of the process of fertilization 

 in the Metazoa, an explanation which I can extend to the 

 Protozoa, now that the long looked for and, indeed, partially 

 observed nuclear fusions accompanying conjugation have been 

 proved by Maupas to be actual facts. Those who do not accept 

 my theory of ids can only maintain that the nuclear fusion of 

 conjugation and fertilization leads to the formation of a new 

 nucleus by the fusion of two equal masses of individually distinct 

 hereditary substance or idioplasm. 



The view which I expressed in 1873, and which has since 

 then been established by Strasburger, O. Hertwig, and myself, 

 of the essential similarity of the male and female sexual cells, 

 can now be confidently extended to conjugation ; for Maupas 

 has already acknowledged the two reproductive nuclei to be 

 essentially similar. They certainly are so, inasmuch as they 

 exhibit no traces of the fundamental antagonism which has 

 been spoken of as a ' male and female principle ' in the egg- and 

 sperm-cell. 



If we may now assume that the nuclear substance which 



