XII.] CONJUGATION AND SEXUAL REPRODUCTION. 183 



frequently compared to the formation of polar bodies in the 

 animal ^gg. If we consider the physiological significance of 

 the two processes, this comparison is certainly striking, but it is 

 incorrect to push it so far as the attempt to homologize the 

 separate phases ' and to explain them as morphologically equi- 

 valent ; for all homology between two living forms depends 

 upon their similar origin, and no one can believe that the 

 higher animals have originated from the Ciliate Infusoria. 

 The kind of conjugation exhibited by the latter is widely re- 

 moved from its simplest form, occurring among the lower 

 Protozoa, and an}' direct connection between the conjugation 

 of Ciliata and the sexual reproduction of Metazoa cannot be 

 assumed. Hence any attempt to homologize the separate phases 

 of these two kinds of amphimixis must fail, although the pro- 

 cesses are in their essence certainly homologous ; for both have 

 sprung from the same root, — the conjugation of the lowest forms 

 of living beings. 



I shall, however, attempt to show that many of the details of 

 the two processes possess a corresponding significance, which 

 must therefore be very deeply rooted, inasmuch as similar 

 events have not been called forth by a common origin but by 

 physiological necessity ; just as the eyes discovered by Semper -^ 

 on the back of certain slug-like Molluscs {Oncidium) resemble 

 Vertebrate eyes, not because the Molluscs have been derived 

 from Vertebrates, or vice versa, but because the necessity for 

 eyes has called forth such a structure out of the foundation 

 provided by the fundamental nature of hght and the histological 

 details of the Oncidium' s dorsal surface. 



I find the foundation of my explanation of the nuclear divi- 

 sions accompanying amphimixis in the fact that the micronucleus 

 of Infusoria possesses nuclear rods or idants, the proof of which 

 we owe to the researches of Pfitzner^, R. Bergh *, Maupas, and 

 Balbiani^. This fact indicates that the structure of the idio- 



' A. Giard, ' Sur les globules polaires et les Homologues de ces 

 elementfe chez les infusoires cilies.' Paris, 1890. 



- C. Semper, ' Ueber Schneckenaugen vom Wirbelthiert^^pus.' 



^ Pfitzner, ' Zur Kenntniss der Kernthcilung von Opalina ranarum.' 

 Morph. Jahrbuch, Bd. XI. p. 454; 1886. 



^ R. Bergh, ' Recherches sur les noyaux de TUrostyla.' Liege, 1889. 



•'' Balbiani, ' Sur la structure intime du noyau de Lo.xophyllunt meleagris.' 

 Zool. Anzeiger, No. 329 and 330 ; 1890. 



