Lhe Migration of Fishes. 37 
Beg cae a 2 ORE PST REA 5 
lil. A STUDY OF THE THEORIES WHICH HAVE BEEN 
ADVANCED IN EXPLANATION OF MIGRATION 
OF FISHES, WITH ESPECIAL REFERENCE Po 
THE MENHADEN AND MACKEREL. 
I. THE WINTER RETREAT: THREE ALTERNATIVES. 
The relations of the temperature of the water to the move- 
ments of the menhaden schools having been studied, a new 
question is at once suggested. When the schools disappear 
from our coast, driven by falling temperatures, where do they 
go? The answer must be in the form of a theory, for no 
one has seen them during their winter absence—at least no 
one has been able to identify the New England and Middle 
States fishes after their departure in the autumn. It is evi- 
dent that there are but three courses open to our coast-fishes 
when it becomes necessary for them to leave inshore: 
1. They may swim out to sea until they find a stratum of 
water corresponding in temperature to that frequented by 
them during their summer sojourn on our coast. 
2. They may swim southward until they find water of the 
required warmth. 
3. They may descend into the abyssal depths of the ocean, 
there to remain for a season in partial or total torpidity. 
II. A DISCUSSION OF THE ARGUMENTS FOR AND AGAINST 
HYBERNATION. 
The last of these theories is the least plausible, from the 
fact that it necessitates the greatest change in habits. The 
susceptibility of the menhaden to slight changes of tempera- 
ture has been pointed out. Hybernation in the oceanic depths 
involves a change to water ten to twenty-five degrees colder 
