MONOTREMATA. 
with asmooth and polished surface, and had 
not the slightest adherence to the uterine pa- 
rietes. 
The specimen containing the two ova next 
in size (fig. 192, cc) was shot in the same 
locality on the 7th of October. These ova 
Measured each three lines in diameter, and 
were situated a little below the middle of the 
left uterus: they were of a spherical form, 
but had evidently been slightly compressed in 
the uterine cavity. They were of a lighter 
colour than the preceding; a circumstance 
which was specially evident at the upper part, 
from the subsidence of the contained vitelline 
Mass. Externally they were sinooth and rolled 
freely out of the position where they were 
lodged, like those of the preceding specimen. 
The third specimen, in the uterus of which 
the largest ovum was contained, was shot on 
the evening on which the first specimen was 
obtained. This ovum had the same spherical 
form, smooth exterior surface, and freedom 
from connexion with the uterus, as in the pre- 
ceding; but was of a much lighter colour, 
Owing to the increased quantity of its fluid 
contents, to which its greater size was chiefly 
attributable. It measured three lines and a 
half in diameter, and had been situated ina 
depression or cell a little below the middle of 
the left uterus. The lining membrane of the 
uterus was highly vascular in the recent state 
in each of the above specimens. 
In all these ova the contents could be seen, 
through the cortical or outer membrane, to be 
of two kinds, viz. a greyish sub-transparent 
fluid, and a yellowish denser mass, which 
varied in their relative proportions as above- 
mentioned, the denser substance always sub- 
siding to the lowest part of the ovum, which- 
ever way it was turned. 
In the largest ovum, the yellow mass or 
yolk occupied about one-third of its cavity, 
while in the smallest it constituted four-fifths 
of the whole mass. 
The chorion or cortical membrane of these 
ova (fig. 193, a) offered a moderate degree 
of resistance when torn open with the forceps, 
and yielded equally in every direction when 
Separated from the yolk, the rent margins 
Fig. 193. 
Uterine Ovum, magnified and dissected, 
Ornithorhynchus. 
( Owen, Phil. Trans. 1834. ) 
397 
curling inwards like the coat of an hydatid. 
This membrane is of a dull greyish colour, 
inclining to brown, slightly transparent, and 
more polished upon its inner than upon its 
outer surface: it resembles the cortical mem- 
brane of the ovum of the Salamander, but is 
of a more delicate texture. The fluid contents 
occupied the space between the cortical and 
vitelline membranes, a situation analogous to 
that of the albumen in the egg of the fowl, 
but had not become coagulated by the action 
of the spirit in which it had been so long im- 
mersed. 
The yellow matter, or yolk, was seen to be 
invested by its proper —— (fig. 193, b), 
which, when reflected under the microscope, 
was found to consist of an extremely thin, 
smooth, and transparent outer layer, which 
I regard as the membrana vitelli (fig. 194, a), 
with a thicker granular membrane immediately 
lining it, analogous to the blastoderma or ger- 
minative stratum (fig. 194, 6). 
The contents of the 
above investments, or 
substance of the yolk, 
consisted of innume- 
rable minute opaque 
granules, similar in size 
and regularity of form 
to those contained in 
the ovarian follicles; 
and with these gra- 
nules were mingled 
larger transparent glo-| ee 
bules of oil. There was! ortion of the ee 
not the slightest trace sum, Ornithorhynchus. 
of chalazz attached to ( Owen, Phil. Trans.1384. ) 
the vitelline membrane, 
as from analogy we might have expected, had 
the ovum been destined to have been perfected 
by incubation. I was unable to detect any 
rudiments of the embryo: an opaque streak 
was discernible on one part of the yolk, but 
not sufficiently definite to be satisfactorily re- 
cognised as a cicatricula; it is indeed, proba- 
ble, from the observation of Lieutenant Maule,* 
that the ova attain a greater size by the im- 
bibition of the nutrient material before the 
lineaments of the foetus become visible. 
The changes which the impregnated uteri of 
the Ornithorhynchus had undergone, as com- 
pared with the same part in the quiescent state, 
were greater than those which have been ob- 
served to take place in the Kangaroo. The 
uterus containing the two smallest sized ova 
measured seven lines in diameter, but was 
much firmer and denser than in the unim- 
pregnated specimens; and having also in- 
creased in length, was thrown into more abrupt 
curves on either side of the ovarian ligament. 
The uterus which had contained the largest 
ovum measured an inch in diameter; and that 
containing those of the second size was of 
Fig. 194. 
* Proceedings of the Zoological Society, 1832. 
** In the insides of several female platypi which 
were shot, eggs were found of the size of a large 
musket-ball and downwards.” 
