THE ORNITHORHYNCHUS PARADOXUS. 225 
The toes on each of the four feet were completely formed, and terminated by curved 
conical horny claws ; but the natatory fold of membrane of the fore foot had not the 
same proportional extent as in the adult, and the spur of the hind foot did not project 
beyond its socket in either specimen. In the smaller one, which was a male, it pre- 
sented the form of an obtuse papilla ; while in the larger specimen, although a female, 
it was more plainly developed and more pointed. his circumstance is in exact ac- 
cordance with the known laws of the development of sexual distinctions, especially of 
those of secondary importance, such as beards, manes, plumes, horns, tusks, spurs, &c., 
which do not avail in distinguishing the sexes till towards the period of puberty. As 
the spur is the only obvious distinction of the sexes in the full-grown Ornithorhynchus, 
I was compelled to refer to the internal essential organs, in order to determine the sex 
of the specimens here described. 
The ventral surface of the smaller specimen was carefully examined with a lens; but 
no trace of an umbilicus could be satisfactorily determined. In the very young or 
newly born Kangaroo, a longitudinal linear trace of the attachment of the umbilical 
vesicle is at that time apparent, but it is rapidly obliterated ; as is probably also the 
case in the Ornithorhynchus. 
In the smaller specimen the intromittent organ projected a little way beyond the ex- 
crementory orifice, as in the young Marsupiata ; but it was not continuous, as in them, 
with the anterior margin of that outlet. In the larger female specimen the correspond- 
ing organ was visible just within the verge of the opening ; but this clitoris, remaining 
stationary in its development, is afterwards, as I have shown in my Paper on the Mam- 
mary Glands*, removed to a distance from the preputial aperture by the elongation of 
the sheath, just as the minute spur of the female lies concealed at the bottom of the 
progressively elongated tegumentary socket, and as the tongue is left at the back of the 
oral cavity by the growth of the jaws. 
The following were the anatomical appearances observable in these young individuals, 
so far as the rarity of the specimens would warrant dissection to be carried. 
On laying open the abdomen in the larger specimen, the most prominent viscus was 
the stomach, which was almost as large as in the adult animal, deriving at this period 
no assistance from the preparatory digestive cavities, the cheek-pouches, which were not 
yet developed. The stomach extended in a curved direction across the epigastric, and 
down the left hypochondriac region to the left iliac region. It was full of coagulated 
milk. On carefully inspecting the whole contents with a lens, no portions of worms 
or bread could be detected; which solves the doubt entertained by Lieut. Maule as to 
whether the mother nourished this young one with the food which was given to her 
for her own support, or with secretion afterwords discovered to escape from the mam- 
mary pores. 
I took a portion of the coagulated substance from the stomach, and diluted it with 
' Phil. Trans, for 1832, p. 525. 
