288 THE EVOLUTION OF THE METAZOA 



separation from the line pursued by the Eumetazoa. Still it 

 may prove useful if we make a closer study of their sex- 

 ual phase; in this way we could make it clear that the form 

 of conjugation ot the sexual phase is not essentially different 

 from a typical copulation. This will finally enable us to propose 

 homologies of the two forms without any greater difficulty. 

 We suppose quite naturally that the descriptive part of the 

 process is well enough known. At the end we intend to touch 

 very briefly on a few final stages of the process of conjugation 

 which as extreme cases, diverge so far from oogamy as the 

 typical sexual form, that a proposed homology might appear 

 less probable if we do not take into consideration the whole 

 development. 



We will first characterize (define) the Ciliata (Infusoria) as 

 they appear if viewed from our standpoint. This definition 

 will agree, I believe, better with the actual facts than do the 

 currently accepted definitions. Infusoria are hermaphroditic, 

 polykaryonic Protozoa whose two karyons are already differ- 

 entiated during the vegetative phase, without free gametes 

 during the sexual phase; the generation of gametes is reduced 

 to a possible minimum; it is at the same time also transferred 

 into the interior of the generation of gamonts (praegamonts) 

 which has made a pairing of the equally sexualized gamonts 

 necessary. The so-called micronucleus represents during the 

 vegetative phase a homologue to the sexual potency of the 

 hermaphroditic primitive sex cell; the micronucleus is equally 

 divided during the vegetative reproduction by means of 

 transverse division; during the sexual phase, however, at a 

 certain moment it divides heterocyclically (unequally) which 

 leads to the formation of gametic karyons of the two sexes, 

 the so-called pronuclei, i.e. the stationary and the migrating 

 nuclei. The gynogamete with its cytoplasm merges totally 

 with the cytoplasm (the plasmodium) of the gamont (the 

 paternal animal) w^hich leads to an internalization of the zygote. 

 The androgamete remains moving actively and it can secon- 

 darily readopt the form of a sperm cell. A new set is developed 



