D. Ward Cutler and L. M. Crump 19 



described by Keeble(9). There is also the remarkable case of the Atlantic 

 Palolo worm (Eunice fucata), which comes out of its hole to liberate the 

 genital segments before dawn on the last quarter of the moon between 

 June 20th and July 25th. H. G. Mayer states that neither the light nor 

 the tide of the last quarter are necessary. 



Further, Bohn in 1904(2) records that sea shore snails taken far from 

 the natural habitat maintain a rhythm synchronous with the tides for 

 a considerable period. 



Each group of the vertebrate kingdom affords examples of the same 

 phenomenon, of which advantage is taken by breeders of mammals; 

 for throughout the whole groups not only the individual, but also the 

 species come "on heat" at periods very nearly identical. That this may 

 be caused by external conditions is probable in certain classes, such as 

 the Amphibia and Reptilia, but in the majority of cases such a con- 

 nection has not been shown and "internal changes of the organisms" 

 are now generally assumed. An excellent discussion of these phenomena 

 is given in Marshall's book The physiology of reproduction. 



Periodicity occurs so widely in all living things that by many people 

 it is regarded as one of the characteristics of living matter. McClendon (10) 

 in discussing the chemistry of vital phenomena says " One striking 

 characteristic of the behaviour of organisms and parts of organisms is 

 their periodicity. The human body shows a periodicity that is perhaps 

 most strikingly demonstrated in fluctuations in temperature, being 

 coldest some time near 3 a.m. and warmest about 10 a.m. Each organ 

 has its characteristic periodicity — respiratory centre 16 and heart 72 per 

 minute, and the motor ganglia 50 per second.... This rhythm must be 

 due therefore to metabolic changes." 



These few examples are sufficient to demonstrate that the periodicity 

 of soil flagellates though so striking, should not be regarded with surprise, 

 but rather as a further example of a wide biological principle. 



Numbers of Active Protozoa in relation to 

 Bacterial Numbers. 



We have reserved to the last the question of the relationship between 

 bacterial numbers and those of active protozoa. Reference to Figs. 1, 3, 5 

 show that it is impossible to establish any correlation between the 

 bacteria and the number of active flagellates; for while these vary 

 rhythmically from day to day the bacteria show no such orderly fluctua- 

 tions. 



2—2 



