474 J. A. DAWSON 



Thus, Neresheimer ('07) and Metcalf ('09) found in Opalina, 

 a parasitic ciliate which has but one kind of nucleus, that a 

 certain type of syngamy took place by the combination of uni- 

 nucleate gametes, the nuclei of which contained chromatin com- 

 parable to that of a micronucleus. In Trachelocerca pheni- 

 copterus, a free-living holotrichous ciliate, micronucleus and 

 macronucleus are merged completely in the vegetative state, but 

 the micronucleus appears during conjugation (Lebedew, '08). 

 Ichthyophthirius multifiliis, a parasitic holotrichous infusorian has 

 a separate macronucleus and micronucleus in certain stages, 

 but in others the micronucleus is contained within the former 

 (Neresheimer, '08, and Buschkiel, '11). Calkins ('12) found in 

 Blepharisma undulans, a free-living heterotrichous ciliate, that 

 the micronucleus is contained within the macronuclear membrane 

 in the ordinary vegetative stages, but becomes separated from 

 the macronucleus during conjugation. 



In the course of experiments on certain hypotrichous ciliates 

 the writer obtained a species of Oxytricha in which, upon stain- 

 ing, no definitive micronucleus was visible. Recalling the work of 

 previous investigators on apparent amicronucleate ciliates where 

 a micronucleus manifested itself during conjugation, it was de- 

 cided to breed the organism and attempt to obtain conjugation. 

 In addition, a culture was carried by the daily isolation method to 

 ascertain the ability of this species to live indefinitely, repro- 

 ducing by division without conjugation. Although careful 

 cytological studies have been made throughout the entire course 

 of the experiments, no definitive micronucleus has at any time 

 been observed, but certain interesting and suggestive results 

 have been obtained. Under conditions favorable to conjugation, 

 the reactions of this organism closely resembled those of a con- 

 jugant, but instead of completing the normal process of fusion, 

 it was found that the animal invariably became cannibalistic, 

 and that there was a strong tendency for pairs to fuse dorsally, 

 thus forming a double animal or 'twin.' 



An account of the investigation of these phenomena will be 

 presented as follows : 



