Marsh — Limnetic Crustacea of Green Lake. 219 



the plankton is very unequally distributed, and that the organ- 

 isms occur in swarms. 



Imhof (Imhof, '92) states that many of the organisms of the 

 plankton occur in swarms. 



Zacharias ('94, p. 129 ff. ) enters into the subject in con- 

 siderable detail, and gives his reasons for believing that 

 the plankton is not uniformly distributed, one of his arguments 

 being the very different character of the plankton at two dis- 

 tant points in Lake Plon, as determined by him. 



Apstein again ('96, p. 51 ff.) takes up the question, and 

 argues it at length, maintaining his original position. 



Reighard ('94, p. 38) concludes that the plankton in Lake St» 

 Clair and Lake Erie is distributed with great uniformity, and 

 finds no positive evidence of swarms. 



Ward in his report on Lake Michigan ('96, p. 62), con- 

 cludes from his study of the plankton of that lake that there is 

 no evidence whatever for the existence of swarms. 



In my preliminary report on vertical distribution in Green 

 Lake (Marsh, '94, p. 809) I stated that apparently the Crustacea 

 were not uniformly distributed. The figures of my collections 

 of the past two years have served to confirm the opinion I ex- 

 pressed in 1894. It seems to me clear, that, so far as the Crus- 

 tacea are concerned, the horizontal distribution is far from uni- 

 form, and inasmuch as the Crustacea ordinarily form the larger 

 part of any plankton collection, it would follow that the distri- 

 bution of the plankton is not uniform. 



It must be remembered that all my collections were made 

 from a buoy kept in one spot during the whole season, and in 

 successive seasons, an attempt was made to drop the anchor as 

 nearly as possible in the same spot. All collections, then, were 

 made from the same depth of water in any season, and in very 

 nearly the same depth in all the seasons. Now, if the distri- 

 bution of the Crustacea were uniform, collections made for 

 the whole depth of water on the same day, or on successive days r 

 should show nearly the same numbers of each species. Of 

 course, if a species were rare, the fact that two or three indi- 

 viduals were found in one collection, and none in the next would 

 not invalidate the assumption of uniformity. Nor even in cases 



