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XV. On the Marsupial Pouches , Mammary Glands , and Mammary Foetus of the 
Echidna Hystrix. By Professor Owen, F.B.S., &c. 
Beceived February 18, — Bead March 2, 1865. 
In the year 1834* it was known that the ovum of the Ornithorhynchus paradoxus left the 
ovarium with a spherical yelk or vitellus about If' (lines) in diameter, and that, having 
reached the uterine portion of the oviduct, it had acquired a smooth subtransparent 
chorion or outer tunic separated from the proper membrana vitelli by a clear fluid. 
Such ova, usually two in number, had been detected in females killed in the month of 
October, in the left uterus, of sizes ranging from to 3^"' (lines) in diameter, without 
any sign of organization of the chorion, or of preparation for placental adhesion on the 
uterine wall. 
The increase of size in the uterine over the ripe ovarian ovum was due to increase of 
fluid between the chorion and vitelline tunics. 
This fluid, homologous with the albumen of the egg of oviparous vertebrates, did not 
coagulate in alcohol, and the only change presented by the vitellus of the largest 
observed ovum was a separation from the “ food-yelk ” of a “ germ-yelk ” in the form of 
a stratum of very minute granules, adhering to part of the membrana vitelli. There 
was no trace of decidua in such impregnated uteri ; the smooth chorion was firmer than 
that of uterine ova of Bodentia ; whence, and for other reasons given in the paper above 
cited, it was inferred “ that the Monotremata are essentially ovo-viviparous.” 
In the same year (1834) I received a young of the Ornithorhynchus paradoxus from a 
nest of that animal, discovered by Lieut, the Hon. Lauderdale Maule in the banks of the 
“ Fish Fiver,” Australia. This progeny, Plate XLI. fig. 5, measured in a straight line 
about 2 inches (other admeasurements will be subsequently given) ; it was naked, blind, 
with short, broad, flexible, and softly labiate mandibles ; the tongue was proportionally 
large, and reached to near the end of the mandibles ; the mouth was not round, as in the 
mammary foetus of marsupials, but in the form of a wide transverse slit ; a pair of small 
nostrils («) opened upon the upper mandible, and between them was a small prominence 
( e ), resembling the knob on the beak of the newly-hatched chick, but softer, and lacking 
the cuticle which had been torn off. There was no trace of navel or umbilical cicatrix f. 
The mouth of this young Platypus, or Ornithorhynchus , was adapted to be applied to the 
flat teatless areola upon which the numerous lactiferous ducts of the parent opened J, 
* “ On the Ova of the Ornithorhynchus paradoxus ,” Philosophical Transactions, vol. cxxiv. p. 555. 
t “ On the Young of the Ornithorhynchus paradoxus,” Zoological Transactions, vol. i. p. 221. 
X “ On the Mammary Glands of the Ornithorhynchus paradoxus,” Philosophical Transactions, vol. c xx l i . p. 517. 
MDCCCLXV. 5 A 
