40 KENDALL: NEW ENGLAND SALMONS. 



were expended in the vain attempt to acclimatize salmonids in waters in which the 

 requisite conditions did not obtain. Even today, although there are volumes of data, 

 they have never been adequately correlated and fish culture and efforts toward ac- 

 climatization are still conducted in much the same bhnd way. 



Granting that all salmonids require cooUng water in which to spawn, how has it come 

 about that the fish are impelled to ascend the rivers from the sea when the same tem- 

 perature may be within as easy or easier attainment in the sea? 



It should here be mentioned that temperature is only a saliently observable factor 

 among perhaps many active, reactive, and interactive factors. The difference of method 

 or degree of response to external conditions shown by different species, is doubtless due 

 to different combinations of factors referred to. While among salmonoid fishes the 

 differences of method and degree are evident, as previously indicated, they are all 

 manifested, as Gurley maintained, in the 'to-cooler migration.' The direction of such 

 migrations is either horizontal or vertical. 



It has already been indicated that the common salmonoid ancestral form was marine, 

 and that, while some of the present forms are beach or shore spawners and have demersal 

 eggs, others periodically ascend the streams as anadromes for procreation. This anad- 

 romy, then, must have originated in the beach-spawning ancestry. The cause must 

 have been the same which determined the present distribution. 



By invoking natural selection, Gurley adduces a logical, though somewhat theoretical, 

 explanation of the formation or evolution of the anadromous habit. He proposes but 

 does not demonstrate a special nerve mechanism which responds or reacts to a down- 

 ward temperature trend. His argument necessarily implies that at sometime during the 

 development of the genitaUa, the 'nerve mechanism' generates in the fish a desire or 

 necessity to seek cooler water which it finds, first near the river mouth, then in the 

 river. Then having obtained the cooler water of the river 'the gear is shifted' so that the 

 motile stimulus is the current of the stream. This in turn signifies another special nerve 

 mechanism which responds to the stimulus of the current. 



Atlantic salmon ascend the same river at different seasons of the year. They avoid 

 some rivers entirely. Some salmon enter a river in the spring, where they linger until 

 near the spawning time at a distance short of the spawning place. It has been stated 

 that in the Rhine some salmon pass the winter and do not spawn until the succeeding fall 

 when salmon which have ascended later are spawning in the same region. Gurley's 

 theory was supposed to apply to aU salmonids whether of the sea or inland fresh waters, 

 and there are instances of so-called 'landlocked salmon' migrating into the outlet at the 

 approach of the spawning season. It is hard to reconcile this fact with the to-cooler- 

 water and head-to-current impulses. Indeed, there is still an unknown quantity, to 

 use a mathematical term. 



The more clearly anatomical structures and their physiological functions are under- 

 stood the more evident it is that organisms of similar structure have similar physiological 

 functions, so it seems that it may be assumed that hke salmonids of like distribution, 

 which migrate to dissimilar places for the purpose of breeding are impelled to those 



