358 



Ayers, Nasal rays in Condylura cristata. 



and by this means to ascertain the immecliate causes of this remark- 

 able sensorial adaptation. Since Talpa may be coDsidered the more 

 primitive form of the two, it becomes a matter of considerable inter- 

 est to traee the developmeut of these fiiiger-shaped processes in Con- 

 dylura. One would naturally expect that in their lirst stag-es of de- 

 velopment; they would simply resemble the ronnded elevations of the 

 papillated tactile surface of the snoiit of such a form as Talpa eiiro- 

 pea-^ the parts of the snout most freqnently broiig-ht in contact witli 

 foreign bodies ultimately developing the papillae to a far greater 

 extent than the remaining portions of the surface. 



CJl.- 



Fig. 3. 



Fig. 2. 



By a gradual elongation of such elevations, to be aecounted for 

 on the principle of adaptation to environment, they would acquire 

 the finger-like form present in Condylura. Their arrangement on 

 the edge of a subreniform diso receives its explanation in the fact 

 that the nerve endings are in this manner placed in a position most 

 advantngeous for the exercise of their special function. 



When we trace the development of the snout in Condylura we 

 find that the assumed method of growth is very nearly an expres- 

 sion of what actually takes place. In the course of the development 

 there arises an interesting complication of the simpler process, the 

 evident meaning of which is the shortening, in point of time of the 

 growth of the papillae, i. e. it is an economic adaptation. This 

 modification I shall now describe. 



At birth the Star-uosed Mole is nearly destitute of visible hair 

 and the tactile bristles of the facial region have not made their ap- 

 pearance at the surface. The snout of the young Condylura lacks 

 all the distinctive characteristics of that 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- 

 boru animal (Fig*. 1) one cau 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 



