OF DIDELPHYS VIRGINIANA. 43 



to flexion and extension, the plane of the sole may sweep through an arc of more than 

 180°, moving from beyond a perpendicular to the axis of the leg, to beyond a parallel 

 with the latter. The other movements of the foot, by whatever name they may be desig- 

 nated, amount to this : that the sole may present perpendicularly inward or outward, as 

 well as horizontally downward, by extent of adduction and abduction ; and the toes may 

 point either inward, forward, outward, or directly backward, by extreme rotation. The 

 first two sets of motions result from the ankle joint alone, but the whole limb is con- 

 cerned in rotation. 



The prehensile tail supplies a "fifth hand." This member is from two-thirds to three- 

 fourths as long as the head and body together ; thick and stout at the base, where there 

 is no very evident point of distinction from the body ; regularly and very gradually 

 tapering to an obtuse tip ; nearly circular on a cross-section, but somewhat flattened 

 underneath, as if by constant pressure. The vertebral articulations and the muscles are 

 so determined that the tail cannot be bent or curled upward, except near its base, where, 

 also, lateral flexion is most marked ; when not in use the tail is habitually carried with the 

 tip curled under, so that it resembles a note of interrogation laid sideways o-. It has 

 also a peculiar power of being twisted upon its axis, particularly toward the extremity, 

 and so winding like a cork-screw around slender supports. The prehensile power is so 

 great that the animal can suspend itself with only an inch or so of the tip of the tail 

 hooked over a branch. Notwithstanding the general similarity of the long naked tail to 

 that of a rat, it does not appear to have by its weight any special function of balancing the 

 body when the animal is moving over uneven surfaces, as a rat's tail is supposed to have ; 

 its use is strictly limited to prehension ; it chiefly comes into play when the animal is climb- 

 ing, and more particularly assists it in gathering fruit from the extremity of the branches. 

 The young attach themselves to the parent's body by the same means. 



Most parts of the body are covered with two kinds of fur. The general covering is a 

 kind of true wool, very fine, short, densely packed, of "kinky " fibre, imbricated and fui^ 

 rowed (scaly-imbricate), and with little or no pigmentary matter. Interspersed through 

 this fur on most parts of the body are numerous true hairs, much longer, straight, stiffish, 

 smooth and cylindrical, uncolored at the base, but loaded with coloring matter on the 

 terminal third or half These hairs are most numerous above, on the sides, and about the 

 root of the tail ; but they are nowhere thick enough to hide the true fur. Below, and 

 on the insides of the limbs the fur alone exists. The hair almost fails on the terminal 

 third of the head ; the extremity of the snout is naked. The fur extends for two inches 

 or more on the tail ; the hairs project a little further. On the extremities the fur stops 

 at the bases of the fingers and toes, and sides of the soles and palms ; but the digits are 

 sparsely hairy. A very fine, soft, short fur clothes the scrotum and lines the marsupium. 

 The whisker-hairs are stout, stiff, straight and very long, but not numerous. 



A few colorless, bristle-like hairs sparsely cover the backs of the fingers and toes, which 

 are otherwise naked, as are the palms and soles, where the integument is thickened and 

 variously modified, forming callosities, etc., or changing into horny plates. (Fig. 1, a, an- 

 conal, and &, palmar, aspect of hand : fig. 2, a, rotular, and 6, plantar, surface of foot ; 

 nat. size.) Above, the digits are covered with somewhat irregular transverse scutella, 

 scarcely overlapping, each divided once or twice across. The palms and soles are stud- 

 ded with small, round, convex tubercles; and the former have six, and the latter five, 



