ORNITHORHYNCHIDA 123 
and the Ornithorhynchus teeth is of the most general character, 
and that the two are certainly widely separated generically, even if 
we do admit that they appear to possess a relationship nearer to 
each other. than to any other known groups of mammals.” 
Reverting to the description of the Duck-bill, we find that in 
the cheeks are tolerably capacious pouches, which appear to be used 
as receptacles for food. The limbs are strong and very short, each 
with five well-developed toes provided with strong claws. In the 
fore feet the web not only fills the interspaces between the toes, but 
extends considerably beyond the ends of the long,“broad, and some- 
what flattened nails, giving great expanse to the foot when used for 
swimming, though capable of being folded back on the palm when 
the animal is burrowing or walking on the land. On the hind foot 
the nails are long, curved, and pointed, and the web extends only 
to their base. On the heel of the male is a strong, curved, sharply 
pointed, movable horny spur, directed upwards and backwards, 
attached by its expanded base to the accessory bone of the tarsus. 
This spur, which attains the length of nearly an inch, is traversed 
by a minute canal, terminating in a fine longitudinal slit near 
the point, and connected at its base with the duct of a large gland 
situated at the back part of the thigh. The whole apparatus is so 
exactly similar in structure to the poison-gland and tooth of a 
venomous snake as to suggest a similar function, but evidence that 
the Platypus ever employs its spur as an offensive weapon has, at 
all events until lately, been wanting. A case is, however, related 
by Mr. Spicer in the Proceedings of the Royal Society of Tasmania 
for 1876 (p. 162), of a captured Platypus inflicting a severe wound by 
a powerful lateral and inward movement of the hind legs, which wound 
was followed by symptoms of active local poisoning. It is not improb- 
able that both the inclination to use the weapon and the activity of the 
secretion of the gland may be limited to the breeding season, and 
that their purpose may be, like that of the antlers of deer and 
many similar organs, for combat among the males. In the young 
female the spur is present in a rudimentary condition, but it dis- 
appears in the adult of that sex. 
The Platypus is aquatic in its habits, passing most of its time in 
the water or close to the margin of lakes and streams, swimming 
and diving with the greatest ease, and forming for the purpose of 
sleeping and breeding deep burrows in the banks, which generally 
have two orifices—one just above the water level, concealed among 
long grasses and leaves, and the other below the surface. The 
passage at first runs obliquely upwards in the bank, sometimes to 
a distance of as much as fifty feet, and expands at its termination 
into a cavity, the floor of which is lined with dried grass and 
leaves, and in which the eggs are laid and the young brought up. 
The food consists of aquatic insects, small crustaceans, and worms, 
