656 MURIDAZ—MUS 
differed somewhat in character. Others have noted more 
vigorous singing by the mice after changes in the weather, 
or when feeding or cleaning themselves, or when in the 
presence of a numerous human company. 
Some observers are disposed to regard the song as a 
sexual call peculiar to some males; it so happens that, if 
we reject as unreliable Mr English’s determination of the 
female sex of a large singing mouse which he saw running 
away, the few cases where the sex has been definitely recorded 
are all males; but really there is no evidence of such a restric- 
tion, and it is difficult to imagine that the occasionally large 
colonies of such mice do not include individuals of both sexes. 
Jackel (in Landois, 1882) thought that the song proceeded 
from a nest of young mice and their parents, clamorous 
with joy at reunion; some have attributed the song to 
contentment, pleasure, or fear; while others, though aware 
that possibly a diseased condition of the respiratory organs 
affords the most likely explanation, have been quite unable 
to detect any trace of disease or weakness in the quality 
of the sounds. Mr English thought that the performances 
of the colony studied by him were of a competitive kind, and 
he attributed the singing to hysteria. Liebe thought that 
the vocal powers of his mouse were due to the presence of 
a membrane in the windpipe which served to straiten the 
aperture. Dr Cohen examined a number of singing mice 
and found traces of inflammation in the windpipes of all; he 
attributed the song to the unhealthy and straitened condition 
of this organ, and regarded the quick mortality, found by 
himself and others among these mice, as further evidence of 
such unhealthiness. Landois also carefully examined a half- 
grown singing mouse. While Cohen heard the song only 
during inspiration, Landois’s specimen emitted sounds 
continuously during both inspiration and expiration—the 
tone was louder and clearer during expiration, weaker during 
inspiration; there were four breaths, and therefore eight 
distinct and quite involuntary sounds per second; the sounds 
were shrill and light, but quite audible across a large room; 
when heard from a distance they were more sonorous, because 
the higher tones of expiration blended with each other and 

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