C. DOBBLL 137 



metazoon. The ciliate is a non-cellular but complete organism : it has 

 a body formed on the same fundamental plan as that of a metazoon, 

 but it possesses no cellular differentiation. Cytoplasm and nuclei are 

 specialized for special functions, but they are not sub-divided into 

 separate units or " cells." 



11. Secondly, it is clear that the moganuclear system of a ciliate 

 is the equivalent of the nuclei of the somatic cells of a metazoon ; and 

 the micronuclear system of a ciliate is the equivalent of the germ-cell 

 nuclei of a metazoon. These homologies — first made clear by Maupas 

 (1889) — rest upon the observed behaviour of the nuclei during conjuga- 

 tion, and at other times in the life-history. It seems to me unnecessary 

 to adduce here all the evidence which can be used to establish this 

 proposition. 



12. Thirdly, conjugation is a process of reciprocal fertilization (in 

 the cytological sense) ; but it is coupled with a process of complete 

 reorganization' unlike anything known to occur in other organisms. 

 The conjugating individuals may be suitably called conjugants, and 

 those which have just conjugated and separated, exconjugants. It is 

 obvious that the conjugant is not a gamete, but a sexual individual: 

 and the exconjugant is a zygote — but of a very remarkable kind ; for it 

 is the remains of the " parent " organism reorganized after the addition 

 of a foreign nucleus. 



13. Fourthly, the migratory nucleus is a microgamete nucleus and 

 the stationary nucleus a macrogamete nucleus. This is evinced by their 

 behaviour before and during conjugation : for the micronuclear divisions 

 which precede conjugation (§ 5) are homologous with the maturation 

 divisions of metazoan germ-cells (§ 7), and the active migratory nucleus 

 is in some (?all) cases of smaller size than the stationary nucleus. 

 {Didinium (Prandtl, 1906), Paramecium (Calkins and Cull, 1907), etc.) 



14. Fifthly, organisms which — like Faramecium — conjugate in the 

 manner described in § 5, must be regarded as hermaphrodite" individuals 

 at the time of conjugation : for they each produce the equivalents of 

 a " male " gamete and a " female " gamete. Organisms which conjugate 

 like Vorticella (§ 6), however, are of a different sexual nature. The 

 large conjugant is a female individual, producing the equivalent of a 

 " female " gamete. The small conjugant is a male individual, producing 

 the equivalent of a "male'' gamete. There is an additional comjalication 



' First definitely stated by Engeimaim (1875). 



'' A conclusiou drawu by Engelmanu (1875) and earlier wurliers, but from incorrect 

 premisses. 



