Chapter V. 



Hatching of Insect Eggs. 



The contents of an egg principally consist of 

 nutriment adapted to the different parts of the 

 germ which it contains — the yolk for nourishing 

 the soft parts; the white, for the blood and other 

 fluids; and the shell, for the bones. In the case of 

 insects, as well as of birds, fishes, and reptiles, the 

 embryo is placed in the most advantageous posi- 

 tion for partaking of the repast, — namely, in a par- 

 ticular corner where it may breathe fresh air always 

 communicated to the chamber of the egg by ven- 

 tilatory passages in the shell; if these be slmt up, 

 by covering the egg with grease, varnish, or chalk, 

 it is suffocated and dies. In the ca.se of birds, 

 according to IMalphigi and the older physiologists,* 

 the rudiment of the chick, wliile still a minute point, 

 is lodged on the film that envelopes the yolk, near the 

 centre of the egg; and, — as the floating wick of a 

 mariner's lamp is constantly preserved upon a level 

 with the surface by the mobility of tiie slings and the 

 weight of the oil-vessel tending downwards, how- . 

 ever the ship move, — there is an ingenious natural 

 mechanism, wliich prevents the embryo chick from 

 being upset when the egg is stirred. The yolk is 

 sustained by two membranous ribbons, visible at tlie 

 aperture of the egg, and fastening it on each side to 

 the common membrane glued to the shell. These 

 suspensory bands being fixed above the centre of the 



* Malpighi, de Ovo incubato , Leciuvenhoeck, Kpist. phys. 

 xl ; and Harvey, in Willougliby's Ornithol. c. iii. 



