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sis of the behavior of the constituent species shows that 43 of the 7 1 

 species (including varieties and forms), 4 of the 6 immature forms, 

 and 10 of the 14 group totals reach their greatest amplitude on the 

 19th, coincidently with the volumetric maximum. Thus, in all, a 

 total of 57 out of 91, or 63 per cent., of the sets of data are in pre- 

 cise agreement as to the time of maximum development. Fur- 

 thermore, of the remaining 35, there are 10 culminating in the 

 collection prior to the 19th (on the 12th), and 16 on the next subse- 

 quent one (on the 26th,) in all, 26 or 29 per cent, which culminate 

 on immediately contiguous dates of examination. This leaves a 

 residuum of only about 8 per cent, which do not exhibit precise or 

 substantial agreement as to the time of maximum development. In 

 the matter of the location of antecedent and subsequent minima the 

 agreement is less pronounced, possibly because the enumeration 

 error is relatively greater in the case of minimum numbers. We 

 find, however, that 65, or 72 per cent., of the antecedent minima 

 of the pulses occur on June 28 or July 5, and 71, or 79 per cent., of 

 the subsequent minima are on July 26 or August 2. Nineteen, or 

 20 per cent., of the antecedent minima are on July 12; and 10, or 

 11 per cent., of the subsequent ones are on August 12. There is 

 thus a residuum of not over 10 per cent, of instances where the data 

 of species or group totals do not coincide or approximate to this 

 pulse, as described, in position of maximum or one or both of the 

 limiting minima. Considering the necessarily large error entering 

 into our data, it is not surprising that exceptions should occur. 

 Some exceptions as, for example, that of Pediastrum pertusum 

 (Table I.) are plainly not due to insufficient data, but are appar- 

 ently normal dislocations; that is, the rhythm of this species at this 

 time is not in harmony with that of the majority of the components 

 of the plankton. . But this is only a temporary derangement, and 

 is not the habitual relationship which movement of production in 

 Pediastrum bears to that of the plankton as a whole. So, also, 

 many of the Entomostraca are much delayed in the culmination of 

 their increase, running over to August 2 or 9, while the most of the 

 other planktonts culminate on July 19 or 26. This lag on the 

 part of the Entomostraca is not, however, habitual, as will be seen 

 on examination of Plates II. and IV. This tendency toward a 

 coincident rhythmic movement in production on the part of the 

 constituent organisms of the plankton will be found throughout all 



