1885.] Recent Literature. 59 
wedge-like head ; while the apparent absence of neck, due to the 
enormous development of muscles in connection with the shoul- 
der-girdle, the retention of the entire arm and forearm within the 
skin, the short and compact body, and the covering of soft, short 
and glossy fur tend to decrease to a minimum the frictional resist- 
ance against the solid medium through which it moves. In fact, 
it presents a most extraordinary model of a machine adapted for 
rapid and continued progress through the earth. 
“The mole does not, and cannot, dig a hole in the same sense 
as other mammals that engage in this occupation, either in the 
construction of burrows or in the pursuit of prey. When a fox 
or a woodchuck digs into the ground the anterior extremities are 
brought forward, downward and backward, the plane of motion 
being almost vertical; while the mole, on the other hand, in 
making its excavations carries its hand forward, outward and 
backward, so that the plane of motion is nearly horizontal. The 
movement is almost precisely like that of a man in the act 
of swimming, and the simile is still closer from the fact that the 
mole brings the backs of his hands together in carrying them for- 
ward, always keeping the palmar surface outward and the thumbs 
below. Indeed, when taken from the earth and placed upona 
hard floor, it does not tread upon the palmar aspect of its fore- 
feet as other animals do, but runs along on the sides of its 
thumbs, with the broad hands turned up edgewise.” 
Regarding the migratory habits of the gray squirrel, which 
have become almost a matter of tradition, the author writes : 
“The minor migratory movements of this species occur with 
more or less regularity from year to year, but on so small a scale 
as to escape general notice. They must not be confounded with 
the great migrations, not rare in former times, when these ani- 
mals, actuated by some unknown influence, congregated in vast 
armies and moved over the land, crossing open prairies, climbing 
rugged mountains and swimming lakes and rivers that lay in 
their path. Though hundreds, and sometimes thousands, per- 
ished by the way, the multitude moved on, devouring the nuts 
that grew in the forests through which they passed, and devas- 
tating the grain fields of the farmer along the route. Though 
these remarkable expeditions have been known and commented 
upon for many years, yet our knowledge of them is limited 
almost to the recognition of the fact of their existence. Scarcity 
of food very probably gives rise to the disquieting impulse that 
prompts them to leave their homes, but the true motives that 
operate in drawing them together, and in determining the direc- 
tion and distance of their journeys are as little understood to-day 
as they were béfore the discovery of the continent on which they 
dwell. 
“In the year 1749 they invaded Pennsylvania in such vast 
hosts as to endanger the crops of the entire inhabited portion of 
