482 J. A. DAWSON 



is apparent that environmental conditions are responsible for 

 many of the so-called life 'cycles' of certain infusorians, and that 

 there is no reason to believe that, given suitable cultural con- 

 ditions, this 'cycle' may not be indefinitely prolonged, or, in other 

 words, that a 'cycle' exists at all. 



2. Atteinpts to obtain conjugation 



As is well known, in the nuclear phenomena during syngamy 

 in all hypotrichida as yet studied, the micronucleus plays the 

 chief part — the macronucleus invariably degenerating and being 

 formed anew from the micronuclei resulting from the division 

 of the synkaryon. It therefore naturally was concluded that a 

 study of this process in Oxytricha hymenostoma would be the 

 crucial test in the attempt to determine the presence or absence 

 of a micronucleus. 



It was soon found that stock animals, if allowed to multiply 

 freely in Petri-dish cultures or on stock slides, after a longer or 

 shorter period of rapid multiplication almost invariably would 

 give evidence of being in the protoplasmic state always observed 

 in conjugating ciliates, aptly described by Calkins ('02) as 

 'miscible.' In such cultures numerous pairs have been observed, 

 fused by the oral surfaces in a manner very similar to that of 

 normal conjugation. In the first stages this fusion was apparently 

 limited to the peristomial membranelles, although many animals, 

 seemingly with very slight attachment, could nevertheless be 

 fixed and carried through the various processes incident upon 

 staining without being separated. In many cases this fusion 

 was not limited to the pellicle, but showed plainly a definite 

 cytoplasmic connection between the members of a pair (fig. 6), 

 but this connection never became quite so extensive as is usual 

 in normal conjugants of other species of hypotrichs. Occasionally 

 pairs have been observed united by the oral surfaces with the 

 bodies of the two animals somewhat twisted around each other. 

 In figure 5 a pair is shown united by the anterior ends in a manner 

 closely resembling that figured by Maupas ('89, fig. 1, pi. 18) as 

 an initial stage in the conjugation of Onychodromus grandis. 



