18 Periodicity in Active Numbers of Soil Flagellates 



In each case the residual acid was determined by titration and found 

 to be approximately constant, and as there had been so little variation 

 in the conditions of working there is no reason to expect any variation 

 in the action on the cysts. Samples 2, 5, 12, 18, 22 in Table I furnish 

 examples. Here the total number of flagellates are nearly identical: the 

 titration values for the. samples are the same, but the number of active 

 flagellates are very different. This also occurs with samples 13, 15, 

 16, 17. 



DISCUSSION. 



Table I and Fig. 3 clearly demonstrate a daily periodicity in the 

 numbers of active forms of the three species of flagellates counted in 

 our experiments. The rhythm is not obviously dependent on temperature 

 or rainfall; for the curves of Fig. 7 show no relationship to the number 

 of flagellates. Nor can we find evidence that any other external factor 

 is the cause. 



Preliminary experiments in laboratory cultures of the organisms 

 maintained at a constant temperature of 20° C. indicate a similar 

 periodicity. Further work on the subject is now in hand, and any 

 detailed discussion of the causes of these daily fluctuations would be 

 premature until more exact knowledge is gained of the life histories of 

 the flagellates and the time required for the completion of each phase. 

 Further, two of the flagellates — Oicomonas and Cercomonas — have two 

 methods of reproduction — an asexual one by binary fission and a sexual 

 one, where conjugation leads to cyst production (li), but little is known 

 of the relationship between these two types of reproduction and the 

 period of time occupied by each. 



It seems safe to suppose, however, that the periodicity is a repro- 

 ductive phenomenon. All through the animal kingdom, from the highest 

 to the lowest class, breeding is a periodic phase, not only of the individual, 

 but also of the species. In the protozoa the malaria parasite affords a 

 good example. As is well known the attacks of fever coincide witn the 

 breaking up of the rosette phase of the parasite into merozites. Hence 

 in the tertian ague, caused by Plasmodium vivax, fever returns every 

 third day, and in quartian ague of P. malariae, every fourth day. Thus 

 in these two species of Plasmodium there is a reproductive periodicity 

 which may be kept up for months. A reproductive rhythm has been 

 suggested in other species of protozoa by Calkins (3) for the fission rate 

 of Paramecium, Woodruff (12) and Gregory (8) for this, and other ciliates, 

 and by Boeck(i) for the encystment of Giardia. In the other phyla of the 

 invertebrate kingdom periodicity obtains as in the egg-laying of Convoluta 



