1903. ] SPIRACLES OF POLYPTERUS. 11 
3. Specimen B repeated the movement, and small bubbles of 
air did issue from the spiracles. 
4, Specimen A repeated the movement, but no air was seen to 
issue from the spiracles. 
5. Specimen B repeated the movement violently after some 
excitement, and as it met the surface widely opened the 
spiracles, forming a triangular aperture, one side being 
the side of the head and the two other sides being the two 
plates of bone which form the spiracular flap; whether air 
passed in or out of the spiracles was impossible to see as 
the top of the head was out of the water. No bubbles 
passed from the spiracle during descent. 
Specimen A repeated the movement, the spiracles did not 
open, and no air was seen to issue from them during 
descent. 
On December 8th I watched them again foran hour.  Polypterus 
A and B came to the surface for air 8 times, and 4 times the 
spiracles were widely opened above the surface of the water, and a 
sound produced as of the sucking in of air. 
T have often found it convenient to kill Polypterus by piercing 
the cranial roof and destroying the brain. During the operation 
it is quite easy to stimulate the brain-centres in such a way that 
the spiracles are widely opened as described above. It is possible 
to stimulate continuously so that the spiracles are retained in the 
widely opened condition. I believe, then, that the spiracles are 
used to take in and to give out air from the swim-bladder. At 
certain times the fish rises quite slowly to the surface in the 
horizontal position, when it would be easier for it to exchange 
the air in the swim-bladder from the surface of the head than to 
turn its head upwards in order to take air by the mouth. By 
closing the mouth and opercula, distending the body-wall and 
opening the spiracles, I believe the fish is able to inhale air, and | 
should suppose that it expires previously during the same move- 
ment, as does Protopterus. I think it possible also that in the 
very shallow water which this fish frequents at certain times 
of year, it may be of use to the fish to change the air in its 
swim-bladder in this way. I have often noticed, in changing the 
water in a tank in which numbers of these fish are confined, that 
when the water is exhausted the spiracles are frequently opened. 
The position of the spiracles almost immediately over the long 
slit-like glottis is in favour of the view that they are connected 
in their functions with the latter. They seem also to be used, as 
I at first believed, to let out the excess of air from the pharynx 
after the fish has taken air into the swim-bladder, either with the 
mouth or with the spiracles. 
Observation upon these points is very difficult owing to the 
rapidity with which the movement takes place; but the fish 1 
have been watching have become very tame, after three years of 
captivity, and these movements are now more slow and much 
more easily watched. 
