CONJUGATION IN BLEPHARISMA UNDULANS 681 



The failure of previous observers to find micronuclei in Blepha- 

 risma uiidulans in the vegetative stages is explained by their 

 formation and retention within the macronuclear membrane. 

 Lebedew ('08) describes micronuclei emerging from the macronu- 

 clei during conjugation of Trachelocerca phoenicopterus, and 

 the observations of Neresheimer ('08) show that some analo- 

 gous process occurs in the parasitic ciliate Ichthyophthirius. 

 The latter observations seem to be inconclusive, and the possibihty 

 at least is open that the new micronucleus does not actually 

 penetrate and enter the old macronucleus, but gives rise to a 

 new macronucleus as in Blepharisma, by secretion. In this 

 connection Neresheimer says : 



The most remarkable thing after encystment is the origin of the 

 micronucleus (Nebenkern), which up to now has invariably been seen 

 in young specimens without any inkling as to where it comes from. 

 It appears suddenly and in a most peculiar manner, when from twenty 

 to thirty fragments are present in the cysts. In sections of this stage, 

 on the inside of the now spherical nucleus, there is a small, highly 

 staining granule which appears like a comet with a tail of plastin and 

 chromatin streaming out behind, connecting it with the nucleus. Soon 

 after, this connecting strand disappears and the complete micronucleus 

 takes a position some distance from the macronucleus. 



Neresheimer does not say that it emerges from the macro- 

 nucleus, but one certainly gets the impression that it is thrown 

 out of the macronucleus. From now on the micronucleus 

 divides with a typical mitotic figure at each division of the 

 cell, while the macronucleus divides by direct division. Ulti- 

 mately the micronucleus divides twice in succession; three of 

 the four resulting nuclei degenerate, the fourth divides again 

 to form male and female pronuclei characteristic of the ciliates. 

 Conjugation occurs not between two cells, but by union of the 

 two nuclei thus formed and the syncaryon then wanders into 

 the old macronucleus where it remains for a time as a karyo- 

 some and finally disappears. 



While it is probable that the micronuclei in these young 

 forms emerge from the nucleus, we need further evidence than 

 Neresheimer brings forward to support the view that the syn- 

 caryon penetrates the old macronucleus instead of forming a 



