stridulation in ants. 911 
becomes more rigid and prominent, and at the spot 
where it is placed over the band, more perfectly regular, 
and so forms a sharper and truer edge. 
The stridulation in Ponerides is performed by drawing 
out the third segment, and at the same time slightly de- 
pressing the hind part of the second segment so that the 
edge of this scrapes over the band ; the beautiful articu- 
lations of the node allow this latter part of the operation 
to be performed with the utmost delicacy, and permit 
the touch of the scraper on the band to be greatly raised. 
In the Myrmicides the operation appears to be carried 
on inadifferentmanner. The scraper is more developed, 
and is placed on the hind margin of the second node ; 
this apparently is held rigid, and the upper surface of 
the following segment is thrown against it, so as to 
bring the band into contact with the scraper; a very 
slight vibration of the hind body will then bring about 
some stridulation. 
It is by no means clear that in the Myrmicides the 
stridulating band is merely a development from the 
general sculpture; it is in some cases excessively diffe- 
rent from this, and the striation has the appearance of 
being developed on a glassy surface poured out on the 
ordinary surface. The scraping ridge is not a direct 
continuation of the hind margin of the segment, but is 
placed on a lower plane. ‘There is, however, one 
Ponerid known to me, fig. 4 (Tasmania), in which these 
parts are in an intermediate condition. Hither that is a 
Ponerid in which this organ has been formed as in the 
Myrmicids, or it is a greater development of the Ponerid 
structure in the direction of the Myrmicids. 
There is great diversity between the different species ; 
this may possibly produce results as great (comparing 
small things with large) as that between the voices and 
song of different species of birds. There is evidently 
considerable difference between the sexes and castes of 
the same species, and I think also between individuals 
of the same caste, but this I have not properly tested ; 
and it will, indeed, probably be found to be very difficult 
to judge of the value of minute differences of structure 
as producing diversity in the vibrations ; if, however, I 
have correctly interpreted the phenomena I| have observed 
in Atta cephalotes, I must conclude that small structural 
differences may be accompanied by great distinctions in 
