212 Animal Music, its Nature and Origin. [ April, 
modified mechanism, began to sing, at first a single note. When 
this grew wearisome and for remedy the pitch was altered, true 
song arose. But the change of pitch could hardly have been at 
a a the first note excited a nerve belonging to a certain 
coherent group, and it was a necessary alternative that the next 
note should excite some other nerve, either within or without 
that group. If within, the combination had occurred mil- 
lions of times; if without, perhaps not once. I cannot doubt 
that the change was within the group; was harmonic; indeed the 
overtones of the first note had already slightly stimulated the 
related nerves, so that their faint tremor extended, as it were, an 
invitation to touch them more firmly. The invitation was fol- 
lowed, and then other similar ones, and finally the song grew 
harmonic, because it followed the easy, preéstablished pathway, 
rising and falling octaves, fifths, fourths and thirds from one to 
another of the many-grouped nerves. He sang to please himself 
or his mate, and the most pleasing combination of notes was that 
most easily heard ; the combination producing least friction and se- 
curing the most economical action of the sound-receiving apparatus. 
In this brief exposition all details are neglected, and even 
inexactness admitted where rigorous truth of statement would 
consume too much space. The more technical treatment of the 
theory, if it can be called that, belongs to physiological acoustics, 
in which province many facts tend to its support. The further 
evidence that can be appropriately presented here, consists of © 
certain statistical proofs gathered from the bird songs which 
occupy the last pages of this article, and it seems very con- 
clusive. 
There are four hundred and six intervals in the thirty-eight 
_ bird songs. Of these, all below the major third may be consid- 
ered as a “filling in ”—material for runs, trills, etc.; they number 
one hundred and eighty-four. 
The major third and the intervals above it are the true pro- 
gressive steps followed by the bird's ear in the long leaps of his 
song; there are of these two hundred and twenty-two. The fol- 
lowing table will show the details: 
{terval pee ag Maj.3d.| gh. (Dim. sth.| sth. (Mi. 6th:| 6th |Dim.geh{ 7th | 8th 
|No. oftones. . 2 | 2% | i 3% t 4% 5 sh eo | 
| Absolute No. =} S | 55 ae Ps ” 60 12 8 we veui S 
| Proportional No. 26 per ct'25 per ct 2 per ct. |27 per ct 6 per ct.|4 per ct. per ct... . |g per ct. 
