V> VICTOR E. -UK!. FORD. 



otherwi-c would have been justified. It is important to recognize 

 how much of the reconstruction is method, and how much is 

 bin]. i^ical principle. 



i. The Biological Principle. The biological principle involved 

 i- one well ivco^ni/'ed, Inn lacking in detailed and definite experi- 

 mental confirmation. It may be stated as follows: Ecologically 

 ci mi iar.d ile animals living under similar conditions possess certain 

 similarities of physiology, behavior, habits and mode of life. 



Indirect evidence for this seems adequate for the purposes of 

 this paper, but we have as yet been unable to conduct experi- 

 mental studies in this line. The process of securing data to 

 illustrate the principles involved here has not been small. 



An obvious difficulty arises in securing language suitable for a 

 brief expression of all that is included in physiology, behavior, 

 habits and mode of life. The term form covers all matters of 

 structure, size, proportion and in common usage, color also. 

 A- opposed to this and as covering all the physiological, and 

 behavior characters just referred to, we will use the Latin word 

 mores. 1 The mores of a species or community of species are not 

 independent of the form or forms: the two are correlated, for 

 every mores, we may expect to find some kind of structure, and 

 for every form of structures, we must also expect to find some 

 physiological differences. Our present methods may not detect 

 these correlations between form and mores and the correlations 

 may not be important, but the existence of such correlations 

 seems to be a necessary assumption. 



In such a series of streams as the north shore streams, it is a 

 well-known tact that the conditions in the young streams are 

 like i hose ( near the headwaters) of the larger and older ones. It 

 was for this reason that this series of streams was selected for 

 the study. Since the same species of fish are present in like 

 condition^, we have evidence for the uniformity ot physiological 

 make up. Since different species occupy different positions in 

 the nicely graded Aeries of complexes, we have an index of their 

 comparative physiological make up which could not be easily 

 deiei led by other means. We have located the animals in their 



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Form .ni'l forms are n-ni in 



