326 J. H. POWERS AND CLAUDE MITCHELL. 



note in that it produced a few conjugants. Early in April this 

 culture became infected with a minute unicellular alga and, pos- 

 sibly as the result of this, the paramecia became more active 

 and increased more rapidly in number. They also ingested the 

 algse until they became greenish in color. On April 15 six pairs 

 of conjugants appeared. Three of these were killed in about the 

 three-hour stage of conjugation, another in about the seventeenth 

 hour of conjugation, while the other two pairs were isolated, 

 allowed to complete the act of conjugation, and the ex-conju- 

 gants used to start new cultures. It was hoped that stronger 

 cultures would thereby be obtained, but this did not follow. 

 They lived and divided slowly for about three weeks only. 



The pairs of conjugants which had been killed were stained 

 and mounted in toto, and are of interest as showing, not only 

 that this type of Paramecium is capable of conjugation, but 

 something of the nuclear phenomena undergone during the proc- 

 ess. In all cases the micronuclei, or at least a part of them, 

 could be made out. In those killed at the three-hour stage 

 (Fig. i) all were in pairs, indicating no doubt the customary 

 divisions preceding nuclear exchange. In one case three of these 

 pairs were really single nuclei in advanced division. With dif- 

 ficulty the nuclear membrane could be made out, extending, as 

 in the case of the larger dividing micronuclei of P. caudalum, 

 between the separating portions of the dividing nucleus. The 

 micronuclei forming the pairs in these three-hour conjugants were 

 smaller than those in non-conjugants. The macronucleus in this 

 stage is still unchanged except that its surface is more or less 

 furrowed. 



In the pair of conjugants killed at the seventeen-hour stage 

 the micronuclei are also present, some again in pairs or in division, 

 some single. The macronucleus on the other hand has now 

 broken up into bands and curved segments, simulating a reticu- 

 lum. This breaking up of the macronucleus at an early stage 

 does not occur with P. caudatum, and, in case further study 

 shows it to be habitual with the present type, this will constitute 

 further proof of its independence. 



The limited number of conjugants at our disposal and the 

 consequent inability to procure all the stages ha\r prevented 



