FROM THE EGG. 225 



On a former occasion, I have already stated before this 

 Board, that all animals, even the highest, mankind not ex- 

 cepted, are reproduced through eggs, and that those eggs 

 have the same structure throughout the animal kingdom. 

 Your idea of an egg will be very incorrect if it is derived only 

 from birds' eggs. Indeed, they are, on the contrary, excep- 

 tional in structure. Few animals produce eggs like the birds. 

 Their egg is surrounded by a hard, brittle shell, and though 

 there are other animals whose eggs have a hard shell, there 

 are very few outside the class of birds, the shell of whose eggs 

 is brittle. The bird lays its egg in the form which it will re- 

 tain until the young breaks through the shell and appears as 

 a living animal capable of providing for itself, or of receiv- 

 ing nourishment from its parents. In other animals the egg 

 grows and increases considerably in size, even after it is laid ; 

 at least, this is the case in many other animals. You may 

 often have noticed it in some of our turtles. Our snapping- 

 turtle lays eggs which are about the size of a small walnut. 

 Examine them during the summer, and you will find that they 

 enlarge to nearly twice the size before the little turtle breaks 

 through ; the hard shell expanding up well as the whole egg. 

 What is so palpable in the egg of the turtle, is more or less 

 so, and may be ascertained without great diflBculty, in the 

 eggs of almost all other animals. If you have ever watched 

 the strings of eggs laid by toads in pools of water by the 

 road-side, you must have perceived that the eggs arc rather 

 small at first, and afterwards acquire a diameter twice as 

 great. So with the fishes. When first laid, the eggs have 

 not half, some of them not one-quarter, the diameter they 

 acquire at a later time, before the young is hatched. Here, 

 then, we have one marked peculiarity of the egg, namely, that 

 it enlarges as it grows. If we except birds, in which the 

 rigidity of the shell prevents any such enlargement, this is true 

 of the eggs of most other animals. 



I will not allude to the different phases in the formation of 

 the egg, as I described them very fully in the lecture last 

 year.; but I must repeat so far as to say, that these eggs, 

 however varied when adult, are identical as to size and ap- 

 pearance about the time when the germ begins to be formed. 

 They are at first microscopically small, growing slowly and 



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