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 if.) 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 Pldn, 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 ali 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, 
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 
