222 Marsh — Limnetic Crustacea of Green Lake. 



As a second principle I would say that only a long continued 

 series of observations on the same body of water will furnish suf- 

 ficient evidence of the uniformity or lack of uniformity in distri- 

 bution. Two or three, or even several parallel, or successive 

 collections do not furnish sufficient evidence. 



Now, in criticising other observers, Fric and Vavra appar- 

 ently determined the amount of plankton entirely by the method 

 of weighing. Reighard and Ward made their comparisons en- 

 tirely by the volumetric method, but in the results of both, 

 there were certain discrepancies which could be most easily ex- 

 plained on the assumption that some of the organisms occurred 

 in swarms. (Reighard, '94, p. 37, Ward, '96, p. 63.) 



Apstein bases his opinion largely on volumetric determina- 

 tions. He also furnishes an enumeration of individuals in three 

 parallel hauls in the Dobersdorfer See, and two sets of two each 

 in the Great PlOner See. These counts show a remarkable uni- 

 formity in the smaller organisms, but there is a considerable 

 variation in the numbers of the Crustacea, the difference being 

 in many cases over 200 per cent. The only criticism one can make 

 of Apstein's work is that the enumerations do not include a suf- 

 ficient number of collections. While apparent uniformity in a 

 few collections would be presumptive proof of a general uni- 

 formity, a single well authenticated case of unequal distribu- 

 tion would overthrow any conclusions founded on such collec- 

 tions. 



Both Apstein and Ward raise the question as to the defini- 

 tion of the term "swarm. " Now, it seems to me, the deter- 

 mination of the fact that limnetic organisms are or are not uni- 

 formly distributed is of first importance, and it makes very lit- 

 tle difference just what meaning shall be attached to the word 

 "swarm," until this question is decided. Without doubt the 

 term has been used without any very exact meaning, as simply 

 indicating a greater or less local aggregation of organisms, 

 with very little thought of the cause of that aggregation, or of 

 the exact or even approximate density of population that should 

 be designated by the term. 



Of course, as the result of my investigations I can speak only 

 of the Crustacea, and not of the plankton as a whole, except as 



