Marsh—Limnetic Crustacea of Green Lake . 223 
the plankton, in many cases, is very largely composed of Crus¬ 
tacea. 
It seems to me that my collections clearly show that so far as 
the Crustacea are concerned, while parallel or successive 
collections may show great similarity in numbers, they may, in 
other cases vary within such wide limits as to make plankton 
determinations unreliable, unless they are made from the aver¬ 
age of a very large number of collections. Inasmuch as it is 
practically impossible to take a sufficiently large number of col¬ 
lections, it follows that plankton collections largely made of 
Crustacea, cannot be taken as giving the exact measure of the 
productiveness of different bodies of water that some authors 
would have us think. We may say, indeed, with reasonable 
certainty, that one lake is much richer than another, but it 
seems to me very doubtful if we can express their relative pro¬ 
ductiveness by any definite numerical ratio. 
LIST OF PAPERS QUOTED. 
Apstein, Carl. ’92. Quantitative Plankton Studien in Susswasser. 
Biol. Centralbl. Bd. 12 pp. 484-512, 608. 
- ’96. Das Susswasserplankton: Methode und Resultate der 
quantitativen Untersuchungen. Kiel und Leipzig. 
Birge, E. A. ’95. Plankton Studies on Lake Mendota. I. 
The vertical distribution of the pelagic Crustacea during 
July, 1894. Trans. Wis. Acad., Vol. X, pp. 421-484. 
Fitzgerald, Desmond. ’95. The temperature of lakes. Trans. 
Amer. Soc. of Civil Engineers, Vol. XXXIV., pp. 67-114. 
France, R. H. ’94. Zur Biologie des Planktons. Biolog. Cen¬ 
tralbl. XIV., Band, pp. 34-38. 
Fri 9 , Ant., und Vavra, V. ’94. Untersuchungen fiber die 
Fauna der Gewasser, Bohmens, IV. die Thierwelt des 
Unterpocernitzer und Gatterschlager Teiches als Resultat 
der Arbeiten an der fibertragbaren zoologischen Station. 
Prag. 
Haeckel, Ernst. ’90. Planktonic Studien. Jenaische Zeitschrift, 
Vol. XXV. Trans, in Report U. S. Fish Commission, 1889- 
91, pp. 565-641. 
