16 STRUCTURE OF THE LEPIDOFTERA 



CHAPTER II 



THE EGG 



I SUPPOSE yon are all acquainted with the general strnctnre of the 

 hen's egg, having dissected several, in yonr own way, many a time. 



Its outer covering, which j-ou speak of as the ' shell,' yon have 

 observed is hard and brittle. It is composed of a calcareous or limj' 

 substance, known chemically as carbonate of lime. If you put 

 some pieces of it into an egg cup, and throw over them a little 

 vinegar or any other liquid acid, you will see them gradually 

 dissolve away, and small bubbles of carbonic acid gas will rise mto 

 the air. Then again, if you take a long and narrow strip of the 

 shell, and hold one end of it in a gas or lamp flame, after a short 

 time that end will become softer, and will glow brightly m the 

 flame, for it is converted into lime— the same substance that is 

 used by the builders for making their mortar—and the bright glow 

 is really a miniature lime light, such as is always produced when a 

 piece of lime is made intensely hot. 



Just inside this shell yon have seen a thin membrane or skin 

 that is easily peeled off the substance of the egg itself. Next to 

 this comes the ' white ' of the egg, which is really colourless while 

 licpiid, but turns white and more or less solid in the cooking. Last 

 of all, in the centre of this, you have noticed the oval yellow mass 

 that is termed the ' yoke ' or ' yolk,' and which contains tlio 

 embi'yo of the future chick. 



Now if you imagine tliis egg to be reduced in size till two or 

 thx-ee dozen of them would be required to form a single line about 

 one uach long, the outer calcareous shell to be entirely removed, the 

 skin or membrane to be converted into a firmer substance. of a 

 horny nature, and, finally, the yolk to be absent and the whole 

 internal space to be filled with the ' white,' you will then have some 

 idea of the nature of the egg of a butterfly or moth. 



