6 APPENDIX: NO. III. 
similar circumstances. Its latest are by no means its lowest flights ; 
even in November I have observed it at such a height that I could 
hardly have seen it, had not mv eye been directed to it by its ery. 
This is the cricket-like chirp which it always makes with incessant re- 
petition when flying high ; whether it also always makes it when flying 
low I cannot recollect, but I rather think not: it calls my attention to 
the animal when it is within a hundred yards or so, frequently giving 
me the first intimation of its presence : it is so readily distinguished by 
its peculiar cadence from the chirp of other bats, that however dark 
the evening, it gives me certain indications of the Noctule. I have 
often greatly astonished my companions, by announcing the approach 
of a Bat, even before it came in sight: for 1t is a remarkable fact 
that most, or at all events many people are unable to bear this and 
similar highly stridulous sounds, as, for instance, that sometimes 
emitted by the opening of a pair of scissors. It is also worthy of 
notice, that for those who hear them for the first time, it is difficult 
to form the least idea from what direction they come; but I 
believe the same thing happens with other kinds of sounds that are 
heard for the first time, and, if I mistake not, it is said to be a 
fact, that the intuitive perception we have of the direction in 
which sounds come, is only acquired by practice and observation. 
However, this subject of the different capabilities of ears is a highly 
interesting one, for as we find that most men are quite unable to 
detect certain sounds which are distinctly heard by others from a 
great distance, and above almost every other sound, so we are led to 
understand how there may be forcible sounds which are inaudible to 
any of mankind, and which nevertheless may be heard at vast distances 
by the species of creature which excited them. In the few insects 
that I know to utter -any sound, it is a stridulous one. I am not 
aware whether or not it is yet understood by what means the Death’s- 
head Sphina raises its cry ; if it were, perhaps similar facilities 
might be discovered in other insects, so as to satisfy us they do utter 
sounds, though they are too shrill and subtle for our ears. May not 
the use of the tragus, or inner ear of Bats be to catch such sounds as 
these, as the exfoliated nose of some species is to detect the rarest 
essences of smells ? For whilst there are some insects of which we 
know how the males are guided to the females, there are still more 
of whose means of finding each other we cannot even guess with any 
degree of certainty: of the first we know the Glow-worm and many 
others use light as a nocturnal beacon. Some exude peculiar odours, 
and some we know to make various kinds of sounds. Of the second, 
viz., those whose means of finding each other we do not at present 
know, may not many be guided by light, odour, or sound, not in a 
condition to be appreciable by our senses, although perhaps there are 
also others which are endowed with some sense unknown tous? But 
to return to our subject: what is the use or object of the incessant 
chirp of the Noctule, and other Bats? It can hardly be to attract 
their mates, nor to collect their fellows, for either of these purposes 
it would probably not be incessant; neither can it be to keep their 
