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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
lated and adapted to each other as the organs of an animal, and the network of 
interrelations forms the chief object of study for such a biological survey. Our 
special problem is to determine just what place the Rotatoria occupy as members of 
this organic whole. For this a study of the group in all its relations will be necessary. 
Such a study will follow some such lines as the following: 
First, the objects of study must be known and described. To this end there must 
be on record somewhere full and complete descriptions and figures of all the Rotifera 
found in the lake, with their correct names. An important preliminary feature of the 
work consists, therefore, in figuring and describing such forms as have been incor- 
rectly or incompletely described or not described at all. On account of the large 
number of minute species found among the Rotifera, and the unsatisfactory work that 
has been done upon many of them, much remains to be accomplished in this line. 
The best method of carrying on this work will consist in studying carefully circum- 
scribed groups — the species of a single genus, perhaps — describing and figuring all the 
species, and going critically over the literature of the group in such a way as to set 
the synonymy in order. Studies of this sort on the genus Monostyla , on Cathypna and 
Distyla, on Metopidia , on Colurus , on the Rattulidce , or, for a much more extensive 
problem, on the Notommatadw, would be exceedingly valuable. 
Lists of all the species found in the given body of water must also be placed upon 
record, in order that the investigator may know with what material he has to deal. 
Such lists, carefully prepared, are also of much interest for a study of the general 
problem of the geographical distribution of the group with which we are dealing. 
The work above characterized must be considered as purely preliminary to the 
main object of study ; the present paper includes only such preliminary matter. The 
distribution of the animals within the lake and the study of the conditions under 
which they live constitute a problem of much greater interest. Most of the species 
of rotifers seem fitted to some special environmental conditions; what these conditions 
are may be determined by observation and by experiment. From the side of observa- 
tion, lists should be kept of Rotifera of the different regions into which a body of 
water maybe divided — distinguishing thus, as is usually done, limnetic species, littoral 
species, bottom species, and swamp species. This classification is, however, much too 
general to give precise results. It should be supplemented by a careful study of the 
Rotifera of regions of different character, with regard to the depth of the water, the 
character of the bottom, and especially with relation to the plant life of the water. 
The rotifers from the Chara beds, Ceratophyllum beds, Naias beds, Potamogeton beds, 
the Cladophora-covered surfaces, should be studied and listed, to see what relation 
there is between the animal and plant life of the lake. A beginning of this work was 
made during the summer of 1898, but in the two months during which the party was in 
the field not enough could be done, in addition to other work, to permit the drawing 
of any conclusions, so that the results will not be presented till further study is made. 
The changes in the character of the fauna with different seasons of the year and 
with variations in climate must be studied as an important feature of the conditions of 
existence. The problem may be attacked more directly under experimental conditions. 
The animals may be kept in laboratory cultures, and suitable changes produced artifi- 
cially in the conditions within these cultures. The results of these changes on the 
life of the animals may thus be observed. Proper control cultures will always be 
necessary in such work. 
The effects of varying conditions in modifying a given single species is a problem 
