THE ORNITHORHYNCHUS PARADOXUS. 227 
rhynchus. But the structure of the ovary, and that of the ovwm both before and after it 
has quitted the ovisac, afford the strongest analogical proof of the intra-uterine deve- 
lopment of the embryo, and at the same time accord with the ascertained fact of the 
mammary nourishment of the young animal ; there being no store of yelk appended to 
the ovum when it quits the ovisac, as in the Bird, where it supplies the place of a mam- 
mary secretion to the newly hatched chick, and where also the voluminous yelk and its 
chalaz@ serve as an essential nidus to the embryo at the early stages of incubation. 
The kidneys were situated far away from the pelvis and high up in the lumbar region. 
This marked deviation from the oviparous type is well worthy of being taken into ac- 
count in the consideration of the nature and affinities of the Monotremata. It is charac- 
teristic of the Mammiferous type of structure, and would seem to be intended to give 
free space for the enlargement of the uterus, and to prevent the kidneys being affected 
by the continued pressure of this viscus and its contents during the latter periods of 
gestation. 
The situation of the kidneys with respect to each other varied in the two specimens : 
in the larger one, the left was a little higher than the right ; in the smaller one, it was 
a little lower : the latter is the ordinary position in the adult. The supra-renal glands 
did not correspond with this arrangement ; but in both instances the right was higher 
than the left, agreeing with the relative position of the testes in the male, and the ova- 
ries in the female. In Man, the large size of the supra-renal glands is noted as a foetal 
peculiarity ; but in the Ornithorhynchus they are of minute size, their greatest diameter 
not exceeding 4th of a line in the smaller specimen here described; and they increase 
in size progressively with the growth of the animal, and ina greater proportion than 
the kidneys ; which increase would appear, therefore, to have relation to the develop- 
ment of the generative organs. There were no traces of the corpora Wolffiana. 
The testes in the small male specimen were situated a little below the kidneys: they 
were of an elongated form, pointed at both ends, with the epididymis folded down, as it 
were, upon their anterior surface. In the female, the ovaries were freely suspended to 
the loins in a similar position, the right being at this period as large as the left: it is 
the persistence of the latter at an early stage of development which occasions the dis- 
proportionate size of the two glands in the adult. The still greater inequality of size in 
the oviducts of the Bird arises from a similar arrest of the development of the one on 
the right side; but both are equal at an early stage of existence. The uteri were straight 
linear tubes, scarcely exceeding the size of the ovarian ligaments. 
The lungs were found amply developed in both specimens ; the air-cells remarkably 
obvious, so as to give a reticulate appearance to the surface, and a resemblance to 
the lungs of a Turtle. They had evidently been permeated by air in the smaller spe- 
cimen. 
The heart in both specimens was of the adult form, with the apex entire ; but the left 
auricle was proportionately larger than in the adult heart, which is correctly figured by 
VOL, I. 24 
