% 
with the fish when collections were made in midwinter from the mud 
in the bottoms of the pools. 
MIGRATION IN FISHES 
Like its relative, Fundulus majalis, Fundulus heteroclitus is 
most normal in activity in moving water. Mundulus majalis, which 
moves in and out with the tides, has been studied by Dr. 8. O. Mast. 
who finds that it is not only prone to move with the tides, but that 
when the outlet to the ocean is plugged, the fish will convey them- 
selves overland by flopping in the general direction of the ocean. 
Mast (5) shows that the fish actually keep their sense of direction 
in the overland course. He concludes that the fish “apparently re- 
member” the location of the outlet. As Mast can find no external 
features which seem capable of guiding, he concludes that the be- 
havior is dependent on internal factors. 
Fundulus heteroclitus migrates to the shallowest pools of the 
salt marshes and travels up streams past the salt water to water of 
a very low salinity. When it is land-locked it stays throughout the 
winter in the mud in the bottom of salt marsh pools. It is significant 
that Fundulus heteroclitus will return to the ocean on the tides in 
the late fall, and that it ceases coming to the marshes when the water 
reaches a temperature of about 45°F. 
Records made with the salinometer and thermometer from No- 
vember, 1914, to August, 1915, show that Fundulus heteroclitus react 
negatively to water of a low salinity when the temperature is below 
45°F. As the temperature rises and the marsh pools and streams 
are increased in salinity by the incoming high tides of spring, the 
fish migrate freely and stay in water which is fresher than they will 
tolerate at colder temperatures. 
Permanent unditched pools contained killifishes (2. leteroclitus 
and I’. diaphanus), eels, sheeps-head minnows (Cyprinodon) and 
shrimps, throughout the entire winter. Field records of the three 
permanent ne four temporary pools observed, showed that during 
November, the fishes attempted to burrow in the bottoms as the tem- 
perature stood between 43°F. and 47°F. In the case of the permanent 
pools whose bottoms are covered with soft mud and finely torn ee! 
grass and sedge, the fish burrowed down to a depth of 6 or 8 inches 
and many remained there in the black oozy mud at a temperature 
ranging from 40°F. to as high as 45°F. On sunny days some of the 
fishes came out and swam around, plainly visible under the ice which 
was sometimes one-fourth to one-half inch thick over the salt pools. 
In the temporary pools where the bottoms are composed. of 
matted and hardened grass bound together with clay, the fish rapidly 
succumb at the onset of cold weather. Specimens with whitened fin- 
edges secured early enough in the morning to be certain that the sun’s 
rays had not materially ‘changed the temperature of their pools were 
Ld 
