si'X IN PRcriozoA 233 



Order Cbojwtricii 



According- to Plate (1886) and Swarczcwsky (1928), Spiro- 

 cboihi of this cpi/.oic group undergoes conjugation by complete 

 fusion between the conjugants, as sho^n in Fig. AH (5 to 8). Nu- 

 clear details were nor fully worked out. 



CLASS SUCTORIA 



Conjugation among Suctoria, which are usually sedentary and 

 without cilia in the adult state, foUow^s the common pattern in regard 

 to nuclear behavior. There are a number of accounts, but the mono- 

 graph by Collin in 1912 provides a review of the literature published 

 up to that time. 



A^'hen epidemics of conjugation occur, individuals of many spe- 

 cies form cytoplasmic "arms," sometimes as long as the animal itself, 

 which extend out from the body in various directions. If one of these 

 contacts a similar extension from another individual, they become 

 attached and pronuclei are exchanged across the "bridge" thus 

 formed. 



Collin recognized two general types of conjugation in this group; 

 one is the common mode of exchange of pronuclei, separation, then 

 reconstitution of the nuclear apparatus from the syncaryon in each 

 exconjugant. In the other type, there is complete fusion with only 

 one "synconjugant" surviving. In this type the two individuals may 

 be equal in size ("isogamy") or unequal ("anisogamy"). 



In Tokophrya cyclopum (Fig. AI), complete fusion occurred. 

 A first micronuclear division (1 to 3) was followed by a second (4). 

 After fusion of the conjugants a division of the syncaryon produced 

 a single micronucleus and a new macronucleus (5, center) w^hile the 

 macronuclei began to degenerate (5, at ends). Reconjugation could 

 occur. In the case illustrated (6) a synconjugant (left) is shown con- 

 jugating w^ith another individual which is the product of a previous 

 reconjugation (right). The latter has two smaller and two larger old 

 macronuclei besides a new macronuclear anlage and three micro- 

 nuclei. In another illustration (not shown here) a larger synconjugant 

 was in conjugation with two normal conjugants. The Suctoria thus 

 show transitions between the type of conjugation common to the 

 Peritricha and the more typical condition of the other Euciliata. 



Note: The literature dealing with conjugation is so extensive that a compre- 

 hensive discussion is out of the question. Instead, a few topics have been 

 selected for longer or shorter comments. 



