of the Ornithorhynchus Hystrix. 361 
been stated may induce others to prosecute the inquiry, and 
render that part of the chain more complete. 
Between it and the bird, no link of importance seems to be 
wanting. 
The great affinity between the male organs of the Ornitho- 
rhynchus and those of birds, is best illustrated by comparing the 
penis of the former with that of the drake, a figure of which is 
annexed. (Plate XII. Fig. 2.) It is six inches long when drawn 
out to its full extent; but, when left to itself, (so great is the 
contractile power of the urethra,) it retracts, and confines the 
whole penis within the verge of the rectum. 
The urethra begins by a blunt end ; and the vasa deferentia 
open into it close to its origin : its sole use, as in the Ornitho- 
rhynchus, is to eject the semen. 
When more of this extraordinary tribe of animals, which, 
although quadrupeds, are not Mammalia, shall have been disco- 
vered, and naturalists thereby enabled to divide them properly, 
the two which I have described will doubtless be arranged 
under different genera; till then, I have thought it best to con- 
sider them as species of the same genus, rather than encumber 
science with an additional name, or attempt to frame generic 
characters from one species only. 
