2 Wisconsin Academy of Sciences, Arts and Letters . 
uniformly throughout the entire depth of the water, which 
reaches about 22 meters. As the period of maximum develop¬ 
ment passes, the Crustacea aggregate in the lower water, declin¬ 
ing in number in the upper and especially in the middle strata. 
In the latter part of May 1896, more than 26 per cent of the 
total catch was found between the depths of 15 and 18 meters 
—these observations having been made in water 18 meters in 
depth—and nearly 21 per cent during the first half of June. 
In 1895, about 17 per cent were found in the bottom water in 
the first part of June, and nearly 16 per cent during the sec¬ 
ond half of that month. At the time these observations were 
made on the history of the Crustacea, it was supposed that this 
swarm of Cyclops died, hut the observations made in 1905, 1906 
and 1907 show that the story is quite different. It appears 
that many, if not all, of these individuals become encysted and 
remain in this condition until autumn. 
On May 22, 1906, the mud was very carefully examined for 
cocoons, but none were found, although many Cyclops were 
caught just above the mud. On June 1, cocoons were found 
in fair numbers and were present in great numbers at all later 
dates. The cocoon is a small oval body, about 0.65 millimeters 
in length and 0.50 millimeters in cross diameter. It is com¬ 
posed of particles of the mud, vegetable debris , etc., which form 
the bottom of the lake in deep water, rather firmly cemented 
together by some adhesive substance. The entire body of the 
Cyclops is concealed by this covering with the exception of the 
abdominal setae, which are readily seen protruding. The ab¬ 
domen of the Cyclops is usually, though not always, flexed, so 
that the setae protrude on the ventral side and toward the an¬ 
terior end. The origin and nature of the cement which holds 
the particles of mud together have not been determined, but it 
should be noted that the particles are firmly agglutinated and 
not merely collected about the animal. The cocoon forms a 
firm coating, which can, however, be dissected off from the 
Cyclops without difficulty. It is not uncommon to find two 
cocoons firmly adhering to each other, and clusters of three or 
four are by no means rare. 
