REPRODUCTION. 189 
of buds, generally from the exterior of the body, possess- 
ing all the essential parts of the parent stock. The buds 
may develop into individuals complete, but not distinct, 
forming, with others like itself, a compound animal, as 
the Coral; or the buds may become detached, giving rise 
to perfect independent individuals, as the Hydra (Fig. 
186). The latter mode closely resembles self - division. 
Rarely, as in the Aphis, those little green insects causing 
“blight,” the budding is internal, and so rapid that the 
tenth generation would number one quintillion. Budding 
in the higher animals produces monstrosities, as double- 
heads, double-thumbs, ete. 
Generation by Eggs is accomplished by the union of 
two dissimilar cells—a germ-cell, or ovum; and a sperm- 
cell; the embryo being evolved from the former.” An 
egg, which is the product of this a 
union, is the lowest possible condi- Ch) 
tion of animal life. It is a globular 
mixture of albumen and oil. <A 
freshly laid Hen’s egg, boiled hard, 
well exhibits the general structure. y 
The outside shell consists of earthy 5. 457—-Theoretical Egg, 
matter (lime) deposited in a net-work 9 Cell s CaRGER en 
of animal matter. It is minutely  @ albuminous pole; p, 
Purkinjean, or germinal, 
porous, to allow the passage of vapor vesicle; w, Wagnerian, or 
and air to and fro. Lining the shell §&°™™*»° 
is a double membrane (membrana putaminis) resembling 
delicate tissue-paper. At the larger end, it separates to 
inclose a bubble of air for the use of the chick. Next 
comes the albumen, or “white,” in spirally arranged lay- 
ers, within which floats the yolk. The yolk is prevented 
from moving toward either end of the egg by two twisted 
cords of albumen, called chalaze ,;"* yet is allowed to rise 
toward one side, the yolk being lighter than the albumen. 
The yolk is composed of oily granules (about z$5 of an 
