398 
nearly the same size (fig. 192). The right 
uterus in all the specimens had become sym- 
pathetically affected, being firmer in texture 
and thicker in its coats. 
The parietes of the impregnated uteri were 
from three to four lines in thickness; an in- 
crease which was principally occasioned by 
the extension of small vascular folds between 
the fibrous and internal coats, which were so 
placed at right angles to these tunics as to 
present an appearance very similar to that of 
the secoud cavity of the stomach of the Por- 
pesse. The fibrous coat was slightly thickened 
near the cervix, and the serous covering was 
separated from it by the ramifications of nu- 
merous large and tortuous uterine vessels. 
There was not the slightest trace of a deci- 
dual or adventitious membrane in the cavity of 
the womb ; and especial attention was directed 
to this circumstance, in consequence of the 
office assigned to it in a recent work,* as mi- 
nistering support to the ova in the higher 
Mammalia, at a period when, like those of the 
Ornithorhynchus, they have no attachment to 
the uterine parietes.+ 
It may, however, be said that the deciduous 
membrane is here represented by the cortical 
or outer covering of the ovum: but this mem- 
brane, though of a denser structure and with- 
out villi, is certainly analogous to the outer 
tunic of the uterine ovum of the Rabbit and 
Bitch, which in then is gradually separated 
from the vitelline membrane by the imbibition 
of albuminous fluid. Now the relative pro- 
portion of the fluid interposed between the 
cortical and vitelline membranes in the small 
and large ova of the Ornithorhynchus, shows 
that the mutual recedence of the two mem- 
branes is effected in the same way. 
If the form, the structure, and the detached 
condition of the ova of the Ornithorhynchus, 
should still be regarded by some as compatible 
with, and perhaps favourable to, the opinion 
that they are excluded as such, and that the 
embryo is developed out of the parent’s body, 
the following objections oppose themselves to 
such an opinion: the only part of the efferent 
tube of the generative apparatus which can be 
compared in structure or relative position. to 
the shell-secreting uterus of the Fowl, is the 
dilated terminal cavity in which, in all the 
specimens above described, the ova were situ- 
ated; and upon the oviparous theory it must 
be supposed either that the parietes of this 
cavity, after having secreted the requisite 
quantity of soft material, suddenly assume a 
new function and complete the ovum by pro- 
viding it with the calcareous covering neces- 
sary to enable it to sustain the superincumbent 
weight of the mother during incubation ; or, 
that this is effected by a rapid deposition of 
the same material from the cuticular surface of 
the external passages; or lastly, according to 
a more recent, but still more improbable sup- 
* Breschet, Etudes de l’Q2uf Humain. 
+ In the recent specimens Mr. Bennett noticed 
besides the ova only a “ mojsture” in the uterus. 
MONOTREMATA. 4 
ition, by a calcareous secretion of the ab- 
tt ie poured out upon the “my ' 
after its ee Me eh ‘ad 
But granting that the egg is provided in any 
of can pi Se the n external co= 
vering, yet from the evidence afforded by the | 
specimens under consideration, the ovum is 
still deficient in those parts of its organization — 
which appear to be essential to successful in= 
cubation, viz. a voluminous yolk to support — 
the germinal membrane, and the 2 
for bringing the cicatricula into contiguity with 
the body of the parent. Add to this, that such 
a mode of development of the foetus requires” 
that all the necessary nutritive material be 
accumulated in the ovum prior to its exclusion. 
Now the bony pelvis of the bird is 
modified to allow of the escape of an 
both large from the quantity of its 
and unyielding from its necessary 
covering ; but whatever affinities of structure 
may exist in other parts of the Ornithorhyn- 
chus, it is most important to the question of 
its generation to bear in mind that it manifests 
no resemblance to the bird in the condition of — 
the pubic bones. v9 
Again, as we have seen that the ova of the — 
Ornithorhynchus have attained a diameter of — 
little more than two lines after having traversed 
the whole of the Fallopian tube, the length of 
which is six inches, and the internal i b 
surface increased by numerous folds, it may — 
be reasonably inferred, from the analogy of the 
Rabbit and other Mammalia, that the ovum 
was of much smaller dimensions when first 4 
bad 
received into the oviduct. But the yolk in — 
Birds and Oviparous Reptiles is invariably the 
product of the ovary, and derives no e. 
ciable increase from the secretions the 
efferent tube, which supply only the albu- — 
minous part of the egg, or the material forthe 
4 
first formation of the chick. If, therefore, the 
gestation of the Ornithorhynchus terminates by 
the exclusion of an egg, as in the Bird or 
Tortoise, the preparatory steps in the formation — 
of the ovum are widely different, for the parts — 
concerned manifest the essential characters of 
the Mammiferous type, and the germ itself has" 
a corresponding structure. 
These facts, it is agreeable to find, are in 
exact accordance with the now ascertained — 
functions of the abdominal glands; for since 
the yolk in the Bird, besides its uses in the 
course of the fetal development, is intended 
as an after-substitute for a mam ion, 
remaining, as it does, but little diminished 
at the close of incubation, it might have been 
concluded, from @ priori physiological dedue- 
tion, that the Monotremes, in which no such sub- 
stitute is required, would approximate the other 
Mammalia in the small size of the ovarian ovam. 
The nature or amount of subsequent devia- 
tions from a true viviparous generation can be 
determined only by future examinations of more 
advanced ova. From the structure of the cor- 
* Geoffroy St. Hilaire, Gazette Medicale, z 
11, 1833, 23 
