1915.] 



INTKODUCTIOK. 



9 



CHAEACTERISTICS AND DEVELOPMENT OF THE YOUNG. 



The young of Scalopus (PI. I, fig. 3) are born hairless. Vibrissse 

 very soon appear on the lips, but hair does not show until the animal 

 is at least a week or ten days old. The fresh, first pelage remains 

 short and grows little until the animal is nearly one- third grown; 

 it is exceedingly fine and silky, and Hes close to the body, giving 

 the animal a smooth, sleek appearance. Two young,^ probably 

 about a week old, from Jackson, N. C, have the general proportions 

 of the body much as in adults. The feet, both fore and hind, have 

 much the same shape as in adults, and are relatively about the 

 same size, though, on account of the bones of the arm thickening 

 rather than lengthening during growth, the 

 fore feet of the young, being relatively more 

 projected from the body, appear at first glance to 

 be relatively very large. The hind feet are rela- 

 tively a little wider than those of adults. The claws 

 of the fore feet are soft and weak, though relatively 

 thick and broad; those of the hind feet are very 

 soft and only sHghtly developed. The external ear 

 appears as a thickening of the dermis into a flat 

 papilla 1.5 mm. in diameter. The center of this 

 is penetrated by a minute auditory opening that 

 seems to be closed by the contact of its sides; as 

 an auditory organ its function is probably exceed- 

 ingly limited. The rudimentary eye appears as a 

 small pigmented spot covered by dermis ; a minute, 

 imperfect opening passes through the dermis to 

 the eye proper, and may be sufficiently penetrable 

 for the animal to perceive hght from darkness; it 

 seems improbable, however, that the eye is sufficiently developed for 

 form perception, and it is probable that with advanced age the sense 

 of hght perception becomes less acute. 



Skulls of young (fig. 1) a week or ten days old distinctly show the 

 sutures between the principal cranial bones; the sutures between 

 the frontals and parietals, however, are now nearly closed. In 

 comparison with skulls of adults, the mastoid region is high and 

 swollen and the zygomata are heavy. The auditory meatus is 

 distinct and more pronounced than in adults, the bullae small, but 

 relatively high and rounded and not so much flattened. The nasals 

 are short and broad, becoming wider posteriorly; the premaxillge are 

 triangular, adjoining the anterior two-fifths to one-haK of the nasals. 

 During the development of the skull the premaxillss push forward 



B2007-103 

 Fig. 1.— Skull of young of 

 Scalopiis aquaticus macJi- 

 rinoides (X 3). [Recon- 

 structed and dra-^vn by 

 the author from speci- 

 mens Nos. SS99and 5900, 

 Field Mus. Nat. Hist.; 

 from Greenway, Ark.] 



1 Alooliolic, No. 7250, U. S. Nat. Mus. 



