227 



usually high), they decline in amplitude, and in November-Decem- 

 ber often fail to appear in the small numbers recorded. In 1894, 

 records are too scanty to be of significance. In 1895 there are 

 three well-defined pulses, and traces of a fourth in August-Novem- 

 ber. In 1896 there are five in May-September. In 1897 there are 

 six in July-December, data during the remainder of the year being 

 insufficient to define the pulses. In 1898 the vernal pulse in June 

 and a feeble one in October are the only ones which appear. The 

 pulses of Bosmina are best defined in the stable low water of the 

 last six months of 1897. During that period they closely approxi- 

 mate in location of maxima and minima the quantitative pulses 

 and those of the chlorophyll-bearing organisms and of the rotifers. 

 (Compare on this point the plates for 1897 in Part I. Kofoid, '03 

 and PI. III. and IV.) . The slopes of the pulses indicate that Bosmina 

 is capable of very rapid multiplication; and their coincidence with 

 other pulses just noted, taken in conjunction with the fact that 

 males and ephippial eggs appear but rarely, suggests that these 

 pulses of Bosmina are immediately dependent, in large part, upon 

 fluctuations in the food supply for their origin and for the varying 

 courses which they run. 



The relations of Bosmina to temperature appear in the facts 

 that all pulses exceeding 5,000 per m. 3 in amplitude occur at tem- 

 peratures above 70, that the vernal rise does not proceed with any 

 rapidity until this temperature is attained, and that the depressing 

 effect of the autumnal decline below 70 is at once apparent in the 

 reduced numbers per m. 3 No constant relation between the pulses 

 of Bosmina and the midsummer heat pulses such as appears in 

 the records of Diaphanosoma can be traced in the occurrences of 

 Bosmina. 



An inspection of the accompanying table, in which the mean 

 monthly Bosmina population per m. 3 of channel water in July-De- 

 cember, 1897 and 1898, is given, and also the total + and - move- 

 ment in river levels for these months in each year, will suggest an 

 intimate connection between stability of hydrographic conditions 

 and the increase of Bosmina. In 1897 the total movement for these 

 months is from five sevenths to one tenth of that in 1898, and in 

 every instance the Bosmina population is also greater by from 7.5 

 to nearly 400-fold in 1897, the more stable year. The means of the 

 six months are 2.03 ft. and a population of 3,691 in 1897 to 5.3 ft. and 



