722 THE AMERICAN NATURALIST. [VOL XXXIII. 
tracts ; but their strong pectoral and dorsal spines, which close 
backward against the body, are kept from doing any harm by 
the strong muscles of this gastric pouch, which compress the 
enclosed fish and prevent the erection of its spines. 
Swimming.— Peculiar in the swimming movements of Polyp- 
terus is the manner in which the head moves freely from side. 
This produces the appearance of a progression more or less 
snake or eel-like, although in general the powerful sweeps of 
the strong tail characterize the progression as fish-like. 
The pectoral fins were never observed to be used otherwise 
than are the pectoral fins of most other fishes, z.e., primarily as 
balancing organs, but partly as organs of progression. There 
is no evidence that Polypterus uses its fins in the manner fig- 
ured by Klaatsch in Gegenbaur’s Festschrift (Vol. III) as organs 
for walking or crawling. The spreading cartilaginous pectoral 
fin rays give a mobility to the pectorals which is strikingly and 
beautifully displayed in a high development of the “ trembling 
movement,” so often seen in the balancing fins of teleosts. 
The long dorsal fin is not always erect when the animal is 
swimming. It can be raised or lowered at will. 
Breathing. — In spite of repeated observations, there is little 
positive evidence that Polypterus comes often to the surface to 
breathe. The evidence which can be presented concerns a 
number of fish, which were confined in a large wicker basket 
partially immersed in the river. In swimming around the nar- 
row limits of this cage the Polypterus would stick its head out 
of water, but no more than would any fish similarly con- 
fined. On one occasion, while fishing a few miles above Dami- 
etta, we saw a Polypterus, about forty feet from us, thrust the 
anterior end of its body six inches out of the water, make two 
or three gasps, and then swim slowly away. But this fish, like 
many others found in the locality, was dying from the increased 
salinity of the water at this point, caused by the unusually low 
Nile and the backing up of the Mediterranean at high tide. 
Although the fish was not often seen taking in air, the fol- 
lowing fact goes to show that a respiratory function is possessed 
by the swimming bladders or lungs. When the fish is opened 
alive, a marked peristalsis may be observed making its way 
