295 



Percina caprodes in the larger percentage. This species was 

 likewise frequently found in lakes and ponds, from which zonule 

 was entirely absent. Their relations to slow and rapid waters 

 seem essentially the same, but while all the collections of ca- 

 prodes were taken from sand and rock, 11 per cent, of those of 

 zonale came from a muddy bottom. 



Indeed, we have, for the first time, in these last two spe- 

 cies, a pair whose ecological records do not seem to correspond 

 quite closely to their associative coefficients — a fact which 

 might be due to a number of collections of these species too 

 small to give a reliable average, or to the influence of ecologic- 

 al factors not covered by the classification of Table VI. Per- 

 cina caprodes was represented by sixty collections, and Etheos- 

 toma zonale by thirty-two; but I have information concerning 

 the relations of the species to the water current for only four- 

 teen collections of the first species and eighteen of the second, 

 and concerning their relation to the kind of bottom for only 

 twenty of the first and nineteen of the second. On the other 

 hand, it seems certain that the local distribution of darters 

 must be affected by many things not referred to in Table VI. 

 -variations in the mere instinct of segregation, in the kind of 

 food preferred, in relations to the temperature and the chem- 

 ical condition of the water, and the time of the year at which the 

 greater part of the collections were made — involving, as this 

 may, similarities and differences of the annual migratory move- 

 ments of the species — and several other like conditions. 



Collections for Ecological Study. 



It has been the object of this paper to test the availability 

 and the usefulness for ecological study, of the data of the care- 

 ful zoological collector, by applying to them a special method 

 of classification and analysis. At the same time, of course, the 

 method itself has been severely tested; and it might have failed 

 completely in this instance' without being permanently dis- 

 credited. 



The unit of this paper is the collection; but this term as 

 here used is highly various in its meaning, and to some extent 



