50 ANIMAL ECOLOGY 



of conditions affecting their prosperity. Leaving out 

 any of these, he is like one who undertakes to make 

 out the construction of a watch, but overlooks one 

 wheel; and by the time he has studied all these 

 sufficiently, he will find that he has run through the 

 whole complicated mechanism of the aquatic life 

 of the locality, both animal and vegetable, of which 

 his species forms but a single element." 



Collecting is an important means of ecological 

 study. This is particularly true in the early stages 

 of such study, but as the student becomes familiar 

 with species and comes to know many of them at 

 sight, less collecting will be necessary, except in the 

 case of very small species and in those studies which 

 depend upon the total catch as a means of securing 

 data, as, for example, the case of plankton organisms. 

 On account of the large number of species, very few 

 students will be able to determine them at sight, 

 but this does not disqualify a student for beginning 

 ecological study. The greatest aid in handling such 

 a varied population is a numbering of the individ- 

 uals, or lots of specimens, consecutively and recording 

 the full data for them in the notebook. The ques- 

 tion arises at once as to how many specimens are 

 to be assigned to one number. No rigid rule can 

 be followed, but in general it is safe to assign a single 

 number to all specimens which agree in all the funda- 

 mental data, as date, place of capture, and exact 

 habitat. And for my own part I number all indi- 

 viduals taken, upon which any special observations 

 are made, as when a Phymatid is taken with a dy- 



