anatomical Structure of the IV ombat. 311 
When once it is established, that the foetus is nourished 
without a placenta, and that the semen is carried directly into 
the os tineas, we are led to enquire where this gelatinous 
matter for the nourishment of the foetus is formed ; it cannot 
be supposed to be secreted from the internal membrane of the 
uterus itself, which is constantly undergoing a change to 
adapt it to the encreased bulk of the foetus as well as of the 
jelly surrounding it. In birds, the albumen of the egg, which 
corresponds with this jelly, is formed in a tube adapted to that 
purpose called the oviduct, and these lateral canals, which open 
into the cavity of the uterus, bear a near resemblance in their 
form to the oviducts of birds ; in the kanguroo they are found 
in the impregnated state to be enlarged, and to have a very 
free communication with the uterus, while the extremity next 
the vagina is rendered impervious ; both of which circum- 
stances induce me to believe that their sole use is to form this 
jelly, and to deposit it in the uterus. 
In the bird, the yolk of the egg is the part first formed, and 
in its passage from the place of its formation, along the canal 
of the oviduct, the albumen is added to it, and the egg is com- 
pletely formed before it receives the influence of the male ; 
but in all the different genera of the opossum tribe impreg- 
nation takes place in the same manner as in the quadruped, 
the small vesicular ovum receiving the influence of the male at 
the ovarium ; it then passes into the uterus, where it is depo- 
sited ; but instead of becoming attached to the coats of the 
uterus by means of a placenta, as in other quadrupeds, the 
gelatinous matter from the lateral canals every where sur- 
rounds it, and supplies the embryo with nourishment. 
