682 PROFESSOR OWEN ON THE MARSUPIAL POUCHES, MAMMARY GLANDS, 
The urogenital canal is 1 inch 4 lines in length, and about 9 lines in diameter : its 
inner surface shows by some coarse wavy longitudinal rugae its capacity for dilatation. 
The rectum was here of great width ; it terminated by a contracted puckered aper- 
ture (m'), in the back part of the beginning of the vestibule, behind the aperture of com- 
munication of the urogenital with the vestibular canal. The distal half of the vesti- 
bule is lined by a denser and less vascular epithelium than the proximal one. 
I conclude from these appearances that the present Echidna had produced two young, 
of which one only was secured ; and that, either, one was left in a nest in the fallen 
hollow tree, while the other was imbibing milk from the pouch ; or that, if she had 
carried a mammary foetus in each pouch prior to her capture, one had fallen out in the 
scuffle that drove her from her place of shelter and concealment. The slight difference 
in size between the right and left mammary glands may relate to the longer continuance 
of the left one in functional activity, after the loss of the young from the right pouch. 
The chief points in the generative economy of the Monotremes which still remain to 
be determined by actual observation are — 
1. The manner of copulation. 
2. The season of copulation. 
3. The period of gestation. 
4. The nature and succession of the temporary structures for the nourishment and 
respiration of the foetus prior to birth or exclusion. 
5. The size, condition, and powers of the young at the time of birth or exclusion. 
6. The period during which the young requires the lacteal nourishment. 
7. The age at which the animal attains its full size. 
In respect to the second point : as Mr. Harms caught the female Echidna with the 
young, about an inch in length, on the 12th of August, she may be impregnated at the 
latter end of June or in July. Females killed in the last week of July and the first 
week of August, in the Province of Victoria, would be most likely to afford the capital 
facts noted under the fourth head ; viz. the impregnated ovum in utero showing some 
stage of embryonal development in the spiny terrestrial Monotreme. As to the hairy 
and aquatic Ornithorhynchus , the impregnated females in which ova were found in the 
uterus, of small size, and prior to the formation of the embryo, were caught on the 6th 
and 7th of October*. Young OrnithorJiynchi , measuring in length in a straight line 
1 inch and ffhs, were found in the nest on the 8th of December. The period of im- 
pregnation is, therefore, in this species, in the locality of the Murrumbidgee River, 
probably the latter end of September or beginning of October. Females captured in 
the latter half of October and in the month of November, would be most likely to have 
ova in utero exhibiting stages of embryonal development. 
On this point I have been favoured with the following letter, one of a kind including 
most which reach me from Australia on the subject, exciting, instead of allaying, 
curiosity. 
* See figure of the impregnated specimen in Philosophical Transactions, 1834, Plate XSY. a, a'. 
