METHODS OF STUDY 323 



control is left undisturbed. The study of reactions to contact has been 

 carried on by the use of pans described in connection with light and tem- 

 perature and with the use of mica chips, leaves, etc. 



In all experiments the containers are divided into several divisions 

 and the number of animals noted in each division counted at each 

 reading. About ten readings are taken, the number being determined 

 by the number of animals used, w T hich is determined by the number that 

 can be observed before they can move any considerable distance. This 

 is a function of the speed of movement, which also determines the fre- 

 quency of reading. Readings should be taken at such intervals as to 

 enable the animals to completely adjust their positions with reference 

 to the conditions in the interim. 



The most effective method of study is that of mixing animals of differ- 

 ent habitats; this removes the necessity of accurate measurement for 

 rough comparison. The degree of accuracy of such experiments is 

 determined almost entirely by the ingenuity and care exercised by the 

 experimentor. Accuracy of measurement can be acquired, but in the 

 case of some factors, such as light, with some difficulty. Such accuracy 

 should, however, be the constant aim of the worker. 



While a high degree of accuracy may be attained in the field in the 

 case of some factors and reactions, it is, in other cases, necessary to 

 perform experiments in the laboratory also. As a rule all experiments 

 should be performed in both field and laboratory. 



(b) To determine the most important activities: The first step in 

 field observation is the continuous watching of animals throughout a 

 number of life cycles. Experimentation is almost always necessary also. 

 It is only under unusually favorable conditions that the relative impor- 

 tance of the various periods of the life history of an animal can be 

 ascertained without experimentation. On the other hand, experimen- 

 tation must be correlated with field observation. Simple experimenta- 

 tion on the behavior of animals in the laboratory does not illuminate 

 this matter to any appreciable extent. 



To determine the habitat preference of animals, they should be placed 

 in cages, in which they find several different sets of natural conditions, 

 and the selection made by the animal noted. 



METHODS OF TAKING A CENSUS 



Species are of importance because each usually has a physiological 

 makeup and habitat preference differing from other species. To make a 

 census of the animals present in a given habitat it is necessary to visit 



