DICROSTONYX 139 



portion of the tail in length. Hands and feet short and broad, 

 each with five digits, the palms and soles densely furred. In 

 the hand, the thumb is reduced to a small vestige which bears, 

 however, a minute, flattened nail; on the palmar side of the 

 thumb is a large polhcal tubercle, two or three times as large as 

 the thumb, covered with horny integument ; the four outer 

 digits are very short and subequal in length, digits II and V 

 being but slightly shorter than digits III and IV. The lateral 

 fingers (II and V) bear long, slender, laterally compressed claws 

 which, apart from their great size and somewhat unusual vertical 

 thickness, do not differ much from those of ordinary lemmings. 

 The claws of the two central digits (III and IV) are extraordinary 

 structures subject to a remarkable seasonal change ; in young 

 specimens and in adults in full summer pelage, they do not 

 differ greatly from those of other lemmings ; but in winter they 

 are very large, sometimes exceeding half an inch in length, and 

 have the appearance of being double, each of the two fingers 

 seeming to bear two enormous claws, one on top of the other, 

 which are separated at their tips by a more or less deep notch. 

 When these differences in the claws first attracted attention, 

 Pallas and other early observers, working with scanty material, 

 were not unnaturally inclined to attribute them to sex; but 

 Middendorff's researches in Taimvrland and in the museums 

 of London and Munich showed that the difference was not sexual, 

 and he was led to suspect that in some way the variation in 

 the form and size of the claws was correlated with the seasonal 

 pelage changes, of which he gave an excellent account.^ Coues in 

 1879 was the first to demonstrate exactly what takes place, and 

 he described the process as follows ^ : — 



" In spring and early summer, these claws [III and IV] do not 

 appear very different from those of Myodes {Lemmus], though averaging 

 larger, more bulbous at base underneath, with the terminal portion 

 slenderer, straighter, and sharper. This bulbous portion underneath 

 grows out simultaneously with increase in length and amount of 

 curvature of the main portion of the claw, until it equals or even 

 exceeds the length of the latter, and is quite as stout, or even stouter, 

 being somewhat broad and pad-like. At this period, it runs the whole 

 length of the claw, from which it is separated by a groove along the 

 sides, and by a notch at the end, both of varying depth. The claw 

 then looks like nearly two claws, one underneath the other. The pad 

 would then seem to gradually sever its connection with the main claw 

 by progressive increase of the constriction marked by the lateral 

 groove and terminal notch, as well as by loosening from the base, when 

 it appears like an e.xcrescence ; it is finally lost. Thus the process 

 . appears to be a periodical one, like the shedding of the horns of 

 ruminants, and not continually progressive with age; and would 

 seem to be connected witli the particularly fossorial habits of the 

 quasi-hibernating animal that digs galleries underground in which to 



■ MiDDENDORFP, Sibirischc Reise, 2, Th. 2, p. 93, 1853. 



• CouES, Monographs N. Amer. Rodentia, Muridae, 1879, p. 248. 



