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 where 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 



Fio. 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 



