The Diurnal Movement of the Crustacea. 477 
plankton Crustacea in the autumn, did not appear in July in 
numbers sufficient to count. A few individuals were present, 
but were not studied. 
One or two specimens of Pleuroxus trigonellus , O. F. M., were 
caught—doubtless stragglers from the bottom. A single Sida 
crystallina was obtained. 
PLANTS. 
No definite work was done upon the plants of the lake, al¬ 
though the water abounded in vegetation throughout the entire 
time of observations. The predominant alga was a species of 
Lyngbya. Large numbers of Anabcena and allied forms were 
also present, and at times, especially in Period II, the lake 
was covered with a scum, which is locally known by the name 
of “working.” The number of algae was greater in the upper 
levels of the lake, although in the lower levels the quantity of 
algae was proportionately much greater than that of the Crus¬ 
tacea. Still, in general, it maybe said that the vertical distri¬ 
bution of plants and Crustacea agree. 
THE DIURNAL MOVEMENT OF THE CRUSTACEA. 
France, in an article on the vertical distribution of the plank¬ 
ton 1 of Lake Balaton in Bohemia, reached conclusions widely 
different from ours. This lake is 76 km. long and 7-J- km. wide, 
but only 11 m. deep in the deepest parts. France found that 
the plankton animals come by night to the surface, begin to de¬ 
scend at dawn to the deeper regions, remain there until early 
in the afternoon, when they begin to re-ascend, suddenly ap¬ 
pear at the surface shortly after sunset, and there remain over 
night. The Claclocera rise first, the Copepoda about an hour 
later, and the same order was followed in their descent. This 
general law was modified by wind, cloud, rain, etc., in various 
ways not necessary to specify. He found that these movements 
were active, as evidenced by the fact that Pediastrum and 
other minute algse remained constantly at the surface. His 
view is that the animals seek the cooler waters. We had ex- 
i R. H. France: Zur Biologie des Planktons. Biol. Cent. XIV , p. 34. Jan. 15,1894. 
