44 KENDALL: NEW ENGLAND SALMONS. 



Wells (1915, p. 276) remarks that: 'There are two general complexes of factors to be 

 considered in an attempted explanation of the reactions of the anadromous fishes, 

 namely, the fish and the environment. Both are made up of physico-chemical factors 

 which are measurable and to a large degree quantitatively. Of the two complexes, that 

 of the Uving organism is least understood and perhaps, because it is much more variable 

 and changing than the environmental complex, which, especially in the case of the sea- 

 water, varies hardly at all. For the fishes to hve normally in the environment there must 

 exist between the two complexes a more or less complete equilibrium.' After further 

 discussion Wells concludes on page 281 that, 'The migrations of anadromous fishes are 

 probably correlated with rhythmic changes in metaboUsm. These alterations in meta- 

 boUc activity are largely the result of internal changes such as occur with the ripening 

 of the sexual products.' 



Well's argument appears to warrant his conclusions, excepting in his speculation per- 

 taining to the ripening of the sexual products. Paton (1898, p. 169) came to the con- 

 clusion that the migration of the fish is not governed by the growth of the genitalia 

 and by the nisus generativus as shown by the fact that salmon are ascending the rivers 

 throughout the whole year with their genitaUa in all stages of development. His investi- 

 gations showed that in fish, on leaving the sea the ovaries varied from 121 to 1439 grams 

 per fish of standard length, but the accumulations of soUds in their muscles and ovaries 

 together is about the same. So he regarded the 'state of nutrition' as the factor which 

 determines the migration towards the river; when the salmon has accumulated the 

 necessary supply of material it tends to return to its original habitat. Paton regarded 

 the salmon as originally a fresh-water fish which has adopted a sea-running habit. 

 This view concerning the state of nutrition is in accord with the views of other investi- 

 gators and indirectly conforms to the conclusion of the previously mentioned authors. 



As previously remarked, doubtless all of the aforementioned factors, temperature, 

 oxygen, specific gravity, state of nutrition, metaboUsm, irritabiUty, volume of water in 

 the rivers, and probably many others are operative in one way or another in the anadro- 

 mous movements of the salmon. It all means, to use the words of Gurley again, that the 

 fish is 'oriented parallel to its environment.' It has been shown that the salmon is 

 restricted to a definite geographic range, which involves temperature Hmitations (cli- 

 mate). All physical, chemical, and biological elements of this 'life-zone' constitute the 

 salmon's environment. The fact that a salmon is restricted to a particular environment 

 means that it has become adapted, in other words physiologically adjusted to it in the 

 evolution of the species through changes of environment brought about by cUmatic 

 oscillations during thousands of years. This signifies that conformity to the conditions 

 thus imposed is the price of existence of the species. As the temperature is the index of 

 climates, so it is of the environment of the salmon, as all the other factors are intimately 

 linked with the temperature factor. This latter is the only one requiring further discus- 

 sion. 



In the foregoing consideration of the factors stated to be, or supposed to be, concerned 

 in the reproductive migration of the salmon, it has been seen that each has not been 



