The redevelopment of heteropolar doublets and monster cells of Oxytricha fallax after cystment.

Heteropolar doublets of the hypotrichous ciliate Oxytricha fallax can encyst, as can monster cells containing multiple copies of at least part of the ciliature. The resulting cysts excyst as heteropolar doublets or monster cells, respectively. Transmission electron microscopy of resting cysts derived from monster cells and from singlets, however, indicates a complete loss of the ciliature - all kinetosomes, ciliary axonemes, and microtubules. Thus, the determination of each ciliature of a monster cell cannot be attributed to the persistence of any visible part of the ciliature. Transmission electron microscopy of monster and singlet cysts suggests that the information for a ciliature may be related to the system of cyst wall grooves and possibly to differentiations in the inner cell membrane which separates the cyst cytoplasm from the cyst wall. The redevelopment of heteropolar doublets upon excystment indicates that the anterior-posterior polarity is independently determined for each ciliature and is maintained through cystment. This polarity is not, however, reflected in a recognizable anterior-posterior polarity of any visible structure of the resting cyst. The number of adoral zones of membranelles (AZMs) may increase or decrease in some excysting monster cells compared with that observed in the encysting cells. Possible explanations for these changes are offered in the Discussion.