AN AMICRONUCLEATE OXYTRICHA 505 



vided an entirely suitable environment be secured. The amicro- 

 nucleate species, Oxytricha hymenostoma, has lived continu- 

 ously under laboratory conditions for over two years. During a 

 considerable portion of this time (July 10, 1917, to April 30, 

 1918) it has been under continuous observation either on depres- 

 sion slides or in small mass cultures in Petri dishes with the 

 possibility of unobserved conjugation or cannibalism precluded. 

 At the present time (April 30, 1918) the animals in these cul- 

 tures give every evidence of being able to live indefinitely. 

 The conclusion, therefore, in this case again, is that the only 

 requisites for the continued existence of this form are favorable 

 environmental conditions. 



The same conclusion is reached from experiments in which 

 every effort was made to induce conjugation. Although no 

 true process of conjugation has been obtained, there is every 

 reason to believe that the organisms have frequently been in 

 a general physiological condition similar to that of conjugat- 

 ing animals. The entire absence of any of the usual nuclear 

 phenomena attendant upon conjugation has confirmed the belief 

 that this form not only possesses no micronucleus, but also is 

 apparently lacking in the chromatinic material necessary for 

 carrying out the process of syngamy. The continued existence of 

 such an organism indicates, therefore, that conjugation though 

 usually taking place in all other hypotrichous forms, may be 

 entirely dispensed with without loss of viability. 



In cases where syngamy has not been observed there are 

 three abstract possibilities (Minchin, '12): first, that it occurs, 

 but has not been seen ; secondly, that it is in abeyance ; thirdly, 

 that it is primarily absent, i.e., has never occurred in the life- 

 history of the form. The fact that syngamy is of such general 

 occurrence in the protozoa renders the first of these possibilities 

 the most probable. In this case, however, there is every reason 

 to believe that syngamy has been repeatedly attempted, but 

 has never been carried out for the obvious reason that this 

 form lacks the nuclear constitution necessary for the process. 

 The fact that periodic attempts to conjugate occur indicates the 

 probability that it has occurred in the past history of this organ- 



