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JOUKNAL OF MAMMALOGY 
possible. Although their unwillingness or inability to fly at once 
renders them rather easy to catch, they try hard to escape by crawling. 
They are very pugnacious and can inflict a decidedly ugly slash with 
their needle-sharp incisors, as I can testify. When touched, they utter 
a shrill, chattering scream of astonishing volume, with the mouth opened 
to the fullest extent. The special formation of the lower jaw enables 
them to open their mouths to even a greater extent than is usual among 
bats, and this character must in some way be connected with their food 
or manner of obtaining it, but upon this point I can shed no light, for 
the stomachs of all those examined were empty. I have never succeeded 
in making a captive mastiff take food, even by placing a variety of 
insects in its mouth, but one of the captives kept by L. E. Wyman 
ate disabled insects, during the night. The bat seemed afraid of bulky 
prey like Jerusalem crickets even when they had been rendered helpless. 
However, if it habitually feeds only upon small fry, then for what is 
that huge mouth? 
Eumops shares with Nyctinomus the distinction of being among the 
most agile of bats while on the ground. With wing tips folded above 
the back so as to be out of harm^s way, they scutter across the floor in 
a sort of gallop, while the action of their ‘‘arms’^ reminds one of nothing 
so much as an “over-hand’^ swimmer. 
I have found that certain bats which spend the summer in the south- 
ern part of California and migrate at the approach of cold weather, 
can go without food for very little more than forty-eight hours without 
dying, and this is as might be expected. They shun the cold and there 
are seldom or never any storms during the summer that continue long 
enough to prevent them from securing at least a little food every night. 
However, those which spend the winter, even in our thermal belt, must 
be of sterner stuff. The winter storms are not precisely warm and often 
last for three days or more. In addition, there may be a solid week 
of cold weather with ice every night, and although this does not distress 
Nycteris, for instance, I do believe that it would keep Eumops indoors. 
Hence,, it is necessary that the mastiffs be able to fast, and fast they 
can. Although not hibernating in the true sense of the word, they 
enter what may be called a voluntary hibernation or torpid sleep. If 
placed in a cool situation, even late in the spring, they become torpid, 
cold, and to all appearances, dead. I kept one thus from November 5 
to December 13, and usually, when examining her daily, I was obliged 
to shift her wings into different positions before I could detect the 
slightest sign of life. However, no matter how cool the day, disturbance 
