BIRDS. 
36’1 
gree, through the pores of those membranes through 
which such a diversity of aliment has already flow- 
ed, it will then open the small vessels of the chick, 
diffuse a general warmth, and convey a nutrimen- 
tal fluid to the heart. The structure of this little 
muscle enables it to open and dilate, for the recep- 
tion of what passes into it on one side, and likewise 
to contract itself for discharging through another 
orifice what has been already received. The mo- 
ment the heart begins to beat, the animal is alive, 
but still continues to receive, by the mediation of the 
umbilic duct, a flow of nutritious juices, whioh it 
transmits into the other vessels, whose branches 
distribute this nourishment through the whole body. 
All those little canals which were flat before, are 
now swelled and enlarged ; the whole substance im- 
bibes a proper aliment, and the chick begins to 
grow. 
It is almost impossible to distinguish, amidst the 
fluids that surround it, the nature of its daily pro- 
gress and changes, till the period when it issues 
from the shell. But let us not omit one precaution, 
equally evident and astonishing, and which is ob- 
servable in the situation of the speck out of which 
the animal is formed. This minute and globular 
particle of matter, which is lodged on the film that 
enfolds the yolk, has always its position near the 
centre of the egg, and towards the body of the dam, 
in order to be impregnated with a necessary warmth. 
The yolk is sustained by two ligaments, visible 
at the aperture of the egg, and which fasten it on 
