330 JAMES EDWARD ACKERT 



The question of what integumentary organs are concerned 

 naturally arises. Organs capable of being stimulated by such 

 condensations would have to meet certain requirements: (1) 

 They must be distributed over the head and flying membranes 

 at least, as' these parts are foremost in flight; (2) They must be 

 superficially located, for stimulations from air condensations are 

 doubtless very slight. 



While no special nerve structures which appear to form the sole 

 basis for the perception of air pressures have been observed by 

 me, yet the presence of large numbers of free nerve terminations 

 (end-knobs) near the surface of the epidermis seems significant. 

 These structures comply with both of the requirements set forth. 

 They are widely distributed over the body and membranes, and 

 their superficial position among the outermost cells of the stratum 

 Malpighii makes them especially well placed for the reception of 

 light touch stimuli. Their number in the epidermis is enormous. 



The superficial nerve rings (and their terminal fibers), though 

 not located as near the surface of the integument as the nerve end- 

 knobs, are so situated about the necks of the follicles as to be 

 affected by even the slightest movements of the hairs. These 

 nervous structures are also widely distributed over the skin and 

 their position is somewhat superficial. Von Frey ('96), in his 

 researches on the sense of pressure in man, has shown that pres- 

 sure nerve fibrils terminate in a ring surrounding the hair follicle, 

 this form of termination serving as an end-organ. This writer 

 states that on" account of the position of the ring, the fibrils are 

 stimulated by any pressure exerted upon the hair. The other 

 nerve endings on hairs of bats are farther from the surface, so 

 that movements of the hair sufficient to stimulate them would 

 probably have to be more pronounced than those produced by 

 condensations of the atmosphere. 



An examination of the anatomical evidence thus indicates that 

 two types of sensory end-organs in the skin of Chiroptera meet the 

 requirements mentioned for the perception of air pressures. 

 These are the free nerve terminations, and the superficial nerve 

 rings of hairs. 



