REPRODUCTION. 
195 
germ-yolk, immediately surrounding the germinal vesicle; 
and the nutritive, or food-yolk, constituting the greater 
part of the mass, by which the young animal in the egg- 
life is nourished. In the latter case, the young come forth 
more mature than wdiere the food-yolk is wanting. 
As to form, eggs are oval or elliptical, as in Birds and 
Crocodiles; spherical, as in Turtles and Wasps; cylindri¬ 
cal, as in Bees and Flies; or shaped like a hand-barrow, 
with tendrils on the corners, as in the Shark. The eggs 
Fig. 164.—Egg of a Shark (the external gills of the embryo are not represented), 
of some very low forms are sculptured or covered with 
hairs or prickles. 
The number of eggs varies greatly in different animals, 
as it is in proportion to the risks during development. 
Thus, the eggs of aquatic tribes, being unprotected by the 
parent, and being largely consumed by many animals, are 
multiplied to prevent extinction. The spawn of a single 
Cod contains millions of eggs; that of the Oyster, 6,000,- 
000. A Queen-bee, during the five years of her existence, 
lays about a million eggs. 
Eggs are laid one by one, as by Birds; or in clusters, as 
by Frogs, Fishes, and most Invertebrates. The spawn of 
the Sea-snails consists of vast numbers of eggs adhering 
together in masses, or in sacs, forming long strings. 
As a rule, the higher the rank, the more care animals 
