94 ANIMAL ECOLOGY 



forms the natural unit or basis for study. All 

 processes which modify or change such an optimum 

 will stimulate the animal, cause responses and 

 adjustments. There are many degrees or stages in 

 the development of these optima which change with 

 the functional rhythms and with the development of 

 the animal. There are those conditions which in- 

 fluence the activity of certain functions or organs ; 

 those which influence the general vital processes in 

 general, the vital optimum; those which appear to 

 condition the best development of certain families, 

 genera, etc. ; and finally those of animal associations. 

 Of course these grade imperceptibly into one 

 another, and a single animal may in its develop- 

 ment, traverse all of these stages in the development 

 of its associational optimum. Optima thus have 

 histories, and their development and laws of trans- 

 formation are of the most fundamental ecological 

 importance (Adams, 1904, 1909; Blackman, 1905, 

 1906; Shelford, 1911, 1912). 



In the selection of these papers I have been guided 

 by several considerations. Studies of common 

 animals are given preference, also those papers 

 which by their method of treatment and point of 

 view are especially suggestive and may act 

 as models for further study, and particularly those 

 papers which treat of the activities from the stand- 

 point of their changes, cycles, modifiability, and 

 development. It is to such papers that we must look 

 for suggestions regarding the methods or processes 

 of adjustment between the animal and the environ- 



