DEVELOPMENT OF THE MONOTREMES AND CERATODUS. 119 
born at a very early stage, and this fact carried with it a series of 
from the ordinary mammals, such as the cat, dog, or sheep. The 
main difference between these latter and the marsupials was that 
es embryo in the uterus before birth had no vascular attachment 
to the walls. There was no blood nourishment passing from the 
parent to the young animal. The egg of the marsupial had, in 
common with that of the higher mammals, a very small amount 
of food yolk -nsmge He then, by the aid of err. 
described the f the egg of the marsupial. But t 
marsupials tly a eebcline arrangement of the membranes, thou ber 
the development of the egg itself was not deeataiiveics. different from 
the development of the higher mammals 
He then passed on to the development of the ceratodus. This 
animal was a representative of a series of animals which once 
and Burnett Rivers; the see the lepidosiren, found in the 
Amazon ; and the thi rd, ne protopterus, found in certain of 
the rivers of Africa. These three formed a class different from 
all other animals, a OG as they possessed gills, and had the 
form of a fish in an adult state, and at the same time they 
possessed lungs. The structure known in other fish as the air- 
bladder became in this fish highly vascular, and the aerated blood 
ening by oxygen did not pass from the air-bladder through the 
system, but passed direct to the heart, and there they had the 
first idiidion of two chambers in the heart, and they had for the 
first time arterial blood in the heart of a fish. Blood was found in 
that time the fish were ripe, the ovaries and testes being nearly 
developed ; but it was not till the beginning of September that he 
found the first eggs of the ceratodus. He spent many weeks hunt- 
ing, and, with the assistance of the blacks, tained up many hundred 
waterholes ‘hefon e he found the eggs. The eggs were Tid upon 
mon newt. The whole development of the ceratodus had a strong 
resemblance to that of the amphibians, and any one who had any 
uaintance with the she nina of a newt would at once 
“yes the resemblance. These eggs were fertilized in the water 
in a similar way to some , species of the torr The eggs he found 
it very difficult to get. They were covered with an enormous 
