230 University of California Publications in Zoology  [Vou.17 
able that the bat is attracted to these insects by the noise which they 
make in crawling about over the ground or, less probably, by air 
currents due directly to the movements of the insects. 
Touch.—For more than a century naturalists have been aware of 
the dexterity with which blinded insectivorous bats when in flight 
avoid obstacles, and the suggestion has been repeatedly made that 
* which makes them cog- 
nizant of the adjacency of objects which they neither see, hear, nor 
ce 
these little animals possess a ‘‘sixth sense,’ 
touch. Many experiments have been carried on in the hope of 
locating this sense. Hahn (1908, p. 191) states that obstacles are 
perceived chiefly through sense organs located in the internal ear, 
basing his belief upon the results of experiments in which the external 
auditory meatus of each bat used was filled with hardened plaster of 
paris. Ackert (1914, p. 329) regards the experiments of Hahn as 
inconclusive, believing that a bat so mutilated might not act in a 
normal manner. 
Ackert (loc. cit.) himself publishes the results of a search made 
for sensory structures in the skin of bats. The species used by Ackert 
were Myotis lucifugus and Myotis subulatus, species not occurring 
in California, but members of our most abundantly represented genus. 
He performed no experiments upon lying material, but confined his 
investigations to the study of prepared sections of the tissues. <A 
review of the literature upon the subject inclined him to the view 
that condensations (pressures) of the atmosphere set up between an 
obstacle and a bat stimulate sensory structures in the integument of 
the bat. These structures Ackert suggests would have to meet the 
two conditions of distribution over the parts of the bat foremost im 
flight, and of superficial location, as stimulations from air pressures 
are doubtless very slight. 
Two types of sensory end organs found by Ackert (1914, pp. 330- 
331) im the skin of bats seem to him to meet the requirements men- 
tioned. The first of these consists of free nerve terminations (end- 
knobs) found in enormous numbers near the surface of the epidermis. 
Second, are the superficial nerve rings (and their terminal fibers), 
which are so situated about the necks of the hair follicles as to be 
affected by even the slightest movement of the hairs. This investiga- 
tor states that the area of the integument supplied by superficial 
nerve rings is insignificant in comparison with the area supplied with 
nerve end-knobs. Likewise, the number of terminal fibers of the 
rings is not to be compared with the enormous number of end-knobs 
in the epidermis. He remarks, finally, that 
