10 



NORTH AMERICAN FAUNA. 



[No. 38. 



and gradually enclose the nasals anteriorly. Most of the cranial 

 bones are anastomosed and the sutures closed before permanent 

 dentition is acquired. The suture between the interparietal and 

 the parietals is the last to close and is the only one which may remain 

 open and distinct in extreme old age. The sutures between the 

 premaxillss and the maxillse and those between the nasals and the 

 maxillse usually remain indistinctly visible until permanent dentition 

 is acquired. 



The writer has examined no very young moles of genera other 

 than Scalopus, but it would seem that the general relationships of 

 characteristics of young to those of adults would be essentially the 

 same in the different genera. Bishop, writing about Gondylura, states : 

 ''The young were probably ten days old, the fur just beginning to start, 

 which gave the skin a dark brown colour."^ The most remarkable 

 difference between young and adults of Condylura is in the snout. 

 The character of that organ in the young has been well described 

 by Ayres, as follows: 



At birth the star-nosed mole is nearly destitute of visible hair and the tactile 

 bristles of the facial region have not made their appearance at the surface. The 

 snout of the young Condylura lacks all the distinctive characteristics of the adult, 

 and the entire body resembles that of Talpa much more than it does its parent. On 

 a close examination of the distal end of the snout of such a new-born animal one can 

 distinguish a tract of skin which covers four-fifths of the circumference of the organ 

 (the part not specially marked off is the median ventral fifth). This dermal tract 

 extends for three millimeters toward the base of the snout and is marked off from the 

 remaining surface by a series of furrows running parallel to the long axis of the body. 

 A series of parallel ridges is thus formed, each ridge being bounded on either side by a 

 furrow. At their anterior and posterior ends these ridges pass gradually into the 

 neighboring smooth surface. By a gradual ingrowth of the bottoms of the furrows 

 each groove is deepened and each ridge suffers a correspondingly increased definition 

 of form, while at the same time the posterior end of each groove grows toward its 

 neighbor on either side. When the grooves have all united there is formed by their 

 union a common groove which nearly encircles the snout and separates the tactile 

 from the remaining surface of that organ. 



Commencing at the posterior margin of the tactile surface and advancing toward 

 the tip of the snout, the grooves deepen and grow toward each other in their bottom 

 portions until they finally coalesce underneath the ridges. The result of this process 

 is the production of free, finger-shaped processes composed exclusively of ectoderm, 

 attached to the anterior end of the snout in the manner already described for the 

 adult.2 



The pelage of individuals of Scapanus, Parascdlops, and Condylura, 

 one-third grown, has much the same compact, sleek appearance as 

 that of Scalopus, indicating a slow and probably entirely postnatal 

 growth. 



1 Bishop, W. L., Trans. Nova Scotia Inst. Sci., vol. 10, p. 349, Oct. 1, 1902. 



2 Ayres, H., Biol. Centralb., band 4, pp. 358-359, 1885. 



