65 
suggests itself that ponds in which the crustacea can be 
produced by the Dubisch method may be too warm for 
the trout or salmon, and that on the other hand if we 
keep the temperature down to the point required by 
the health of the fish, it may be impossible to rear their 
food. Dr. Kochs of Bonn, has advised that this diff- 
culty be avoided by growing the crustacea in shallow 
ditches connected with the cool pond or brook in which 
the fish live, and into which the crustacea will be 
washed by the currents created by the rise and fall of the 
water, his idea has been elaboratediby Mr. yKazl 
Wozelka of Prague, in a little book recently published, 
entitled “‘ New Methods of Fish-breeding combined with 
Willow culture,” in which he presents several plans, 
worked out in minute detail, of systems of breeding 
ditches and basins connected with ponds and with 
brooks, claimed to be drawn from his own experience. 
Some such system would probably prove practicable. 
leis quite possible that the identical species oi 
crustacea grown in the carp ponds might not thrive in 
water cool enough for trout, but there are others that 
surely would. Many copepods are found in early spring 
in very cool pools, sometimes at Craig Brook even 
anticipating the disappearance of the ice, and several 
species of daphnids occur in active condition in the 
depth of winter. The careful observations on the 
occurrence of aquatic animal life during each day of the 
year ending Oct. 31, 1893, at the biological station at 
the lake of Plon in the northern part of Germany, dis- 
closed the presence, in abundance, of several species of 
entomostraca during every month of the year. From 
January to April, inclusive, there was the greatest 
scarcity, yet no less than seven species of etomostraca 
were abundant in mid-January, and with the exception 
of the period from March 20 to April 10, there was no 
part of the entire year when some species was not found 
in abundance. 
