GROWTH WITHIN THE EGG 
15 
Growth within the Egg. — Food Provisions. The ferti¬ 
lized egg cell must grow to produce the young animal, and 
must, therefore, be supplied with food. What we call an 
egg is commonly the egg cell surrounded by its food material, 
and all is inclosed in a shell. Occasionally it is the egg cell 
alone. If the young animal has, when it is little grown, the 
power of getting its own food, the egg is comparatively small, 
and the young is hatched small and poorly developed. The 
butterfly, an example of this kind, lays her eggs on the leaf of 
some plant, so that the young are in contact with their food 
when they hatch, and have only to open their mouths and 
eat. Most insects follow a similar practice of laying their 
eggs on a food substance. Frogs’ eggs hatch in the water, 
and the tadpoles swim to a soft water plant to which they 
cling and on which they feed. 
If, on the other hand, the young animal must be well 
developed before it is prepared to come out of the security of 
the shell, the egg is large, containing a sufficient quantity of 
food material for the growth of the young. Birds and rep¬ 
tiles are animals of this kind. They lay few eggs compared 
with the hundreds of thousands of small eggs which a fish 
lays, and they usually take better care of their eggs and of 
the young. Birds keep their eggs warm by sitting on them, 
and reptiles bury theirs in a warm place. 
1. What do many eggs contain besides the germ cell? 
2. How does the butterfly prepare for feeding her young? 
3. What means of sustenance have newly hatched tadpoles? 
4. Why need birds’ eggs be so much larger than fishes’ eggs ? 
5. Discuss the significance of the fact that a robin lays three 
or four eggs while a quail lays fifteen or more. 
Embryo Respiration. The young animal, embryo, growing 
within the egg needs oxygen as well as food, but the oxygen 
cannot be stored within the egg; it must be brought in from 
the air continuously as it is needed. If the embryo is very 
