ORNITHORHVNCHIDZ 121 
who have had the opportunity of investigating this question by the 
aid of a good series of specimens have come to the conclusion that 
there is but one, and no traces of any extinct allied forms have yet 
been discovered. 
The length of the animal when full grown is from eighteen to 
twenty inches from the extremity of the beak to the end of the tail, 
the male being slightly larger than the female. The fur is short, 
dense, and rather soft to the touch, and composed of an extremely 
fine and close under-fur, and of longer hairs projecting beyond 
this, each of which is very slender at the base, and expanded, 
Fic, 32.—Platypus or Duck-bill (Ornithorhynchus anatinus), From Gould's Mammals of 
Australia. 
flattened, and glossy towards the free end. The general colour is 
deep brown, but paler on the under parts. The tail is short, broad, 
and depressed, and covered with coarse hairs, which in old animals 
generally become worn off from the under surface. The eyes are 
small and brown. There is no projecting pinna or ear-conch. The 
mouth, as is well known, bears a striking resemblance to the bill of 
a Duck. \It is covered with a naked skin, a strong fold of which 
projects outwards around its base. The nostrils are situated near 
the extremity of the upper surface. There are no true teeth in the 
adult, but their purposes are served by horny prominences, or 
cornules, two on either side of each jaw—those in the front narrow, 
longitudinal, sharp-edged ridges, and those behind broad, flattened, 
