498 BIOLOGY OF THE PROTOZOA 



very generally accepted by protozoologists, the fusing nuclei of 

 conjugating ciliates are interpreted as the nuclei without cell bodies 

 of gametes, such as those of Ophryncystis. An interesting observa- 

 tion by Dogiel (1923) on the parasitic ciliate Cycloposthium bijjal- 

 matum and in other Ophryoscolecidw as well (Dogiel 1925) lends 

 some suj)p()rt to this theory. Here gametic nuclei are formed as 

 in other ciliates; one of these nuclei, the migrating nucleus, develops 

 a tail and, like a spermatozoon, makes its way through the mem- 

 brane of the peristomial region of the mother-cell, and into 

 the external chamber formed In- the mode of fusion of the two 

 gamonts (Fig. 207). From this chamber it enters the other gamont 

 by way of the mouth and ultimately meets and fuses with the sta- 

 tionarv nucleus of this gamont. 





%r 



1 



Fig. 207. — Cydopoathium bipabnatum. f "onjugating individuals with spermatozoon- 

 like wandering nucleus. (After Dogiel.) 



{h) Tsogamctcs and Anisogametes.— The term copulation as 

 used in connection with the Protozoa refers to total and permanent 

 fusion of gametes. Of these there is the greatest variety of struc- 

 tures and differences in different types of Protozoa. In very few 

 cases of isogametes do we find copulation between individuals 

 whose differentiations are not expressed by morpht)l()gical charac- 

 teristics. In such types the individuals differ little if at all from 

 the ordinary vegetati\'e forms except in a physiological sense. 

 Plastogamy or casual cell fusion is easily mistaken for such holo- 

 gamic copulation and descriptions of so-called fertilization processes 

 in Noctiluca, in testate and in naked rhizopods, in Heliozoa and in 

 different types of flagellates are open to criticism on this ground. 

 In the case of Scytonionas {Coprovumas) svhtHis (Dobell K08) and 

 <S. 7ninor (Berliner 1919) the evidence appears to be fairly convinc- 

 ing that copulation of hologametes actually does occur, but even in 

 these cases, the interi)retation is not above criticism (Fig. 208). 



