6 
VERTEBRATA. 
THE GOLDEN OXUOLE : ILLUSTRATION OF PAIRING AND NEST-BUILDING. 
birds' nests, can generally tell at a glance the species to which a particular nest belongs. The 
number of eggs laid is also very uniform in each species. 
In the structure and development of the egg, we find a great uniformity throughout this class, 
the development of the embryo taking place here in precisely the same manner as in the reptiles. 
But notwithstanding this general uniformity in the processes of reproduction, there is a remark- 
able difference in the condition of the young birds at the moment of hatching, and this has given 
rise to the division of the class into two great sections. In some, which usually reside upon the 
ground, where they form their nests and hatch their young, the latter are able to run about from 
the moment of their breaking the egg-shell, and the only care of the parents is devoted to pro- 
tecting their offspring from danger, and leading them into those places where they are likely to 
meet with food. The others, which in fact constitute the majority of the class, pass more of 
their time in the air, and generally repose upon the trees, or in other elevated situations, where 
they also build their nests, and the young birds for some time after they are hatched, remain in 
the nest in a comparatively helpless state, their parents bringing them food, and attending upon 
them most assiduously until their feathers are sufficiently grown to enable them to support them- 
selves upon the wing. A chicken or a partridge, a day after it is hatched, will run about and 
pick up seeds, separating them from the gravel among which they lie, while the young of the 
tree-birds remain often a month in the nest, receiving without discrimination what is given by 
their parents. This diflference between the young of the two classes will be more apparent by a 
glance at the engravings pages T and 8 . The first represents a young curlew, a day or two old, 
going forth with all hip faculties awake, and almost ready to make his way in the world ; the other 
