No. 467.] . ZOOLOGICAL MATERIAL. 783 
6.  Vorticella is often found on decaying duckweed, Riccia, 
and Ceratophyllum. Place a large handful of the material in a 
bacteria dish nearly filled with water. Vorticella often appears 
in cultures prepared for other purposes. 
7. Carchesium often occurs on water snails and crustaceans 
amongst duckweed and Riccia. Collect in the same manner as 
Vorticella, 
. 8. Volvox has been found to occur most abundantly amongst 
duckweed and Riccia, in pools or small ponds that do not dry up. 
Collect this material by dipping it up together with a little of the 
water and place a small handful of the material, with some of the 
water, in each of many bacteria dishes and add enough tap water 
so that the dishes are nearly full. Place the dishes so that one 
side is strongly exposed to light. After a few hours, specimens 
of Volvox may be seen with the naked eye, or with a hand lens, 
at the water’s edge on the lighted side of the dish. Remove 
them with a pipette to a small covered dish filled with clean 
water. . Volvox kept in clear water and strong light seeks the 
bottom of the dish, and can readily be found and removed with 
a pipette when wanted.. If left in the original dish, there may 
be present small crustaceans which will eat them; yet Volvox 
may sometimes be collected from these dishes for several days. 
Usually the material yields best after a day or two, and in three 
or four days becomes worthless. If obtained free from the 
animals that prey upon it, Volvox may be kept for several days 
or even longer. 
Volvox is not always present in localities that seem favorable 
for it, and ponds that contain it in abundance are somewhat rare. 
In some situations it may be collected to advantage by sweeping 
a bolting-cloth net over water plants, or, better, using a “ Birge 
net," which has a coarse net over the top for keeping out large 
forms and trash. ; 
Volvox may be preserved in 4 % formalin. Formalin speci- 
mens show flagella better than living ones. On account of the 
uncertainty of obtaining Volvox late in the fall, a supply of pre- 
served specimens should be laid in early in the season. — 
In studying Volvox, mount the specimens in hollow slides or 
on ordinary slides with cover-glasses supported by fine glass 
rods or by bits of broken cover-glass. ipi : 
