342 



about one-half the length of vibrissae and similar to the long hairs 

 of the pelage; C, short downy hairs closely resembling those which 

 coQstitute the general covering of the body. A deep section through 

 this protuberance in the mole, taken parallel with the surface, dis- 

 closes cross sections of the characteristic tactile hairs with their enor- 

 mously developed blood sinuses, cross sections through the other two 

 classes of hairs, and parts of sebaceous glands and other structures 

 commonly found in the mamalian skin. Such a section shows an ex- 



T T 



Fig. 1. Protuberance of Mole. Fig. 2. Protuberance of Rat. 



Fig. 1 — 4. Protuberances of mole, rat, white-footed mouse, and bat, respec- 

 tively. X 5. T. tactile hair. 



tremely crowded condition of the structures immediately surrounding 

 the tactile hairs, as contrasted with the more widely separated blood 

 vessels, hairs, glands, etc., in the periphery of the organ. The massing 

 of the tissues is no doubt largely caused by the remarkable develop- 

 ment of the vibrissae and their respective blood sinuses. There is, 

 too, a marked increase in the amount of connective tissue here, which, 

 however, may be accounted for by the need of greater support for 

 the roots of these large tactile hairs. Thus it is altogether probable 

 that the unusual size of both the roots of the tactile hairs, and of 



