2()6 PHILOSOPHY OF ZOOLOGY. 



cases, each species has a peculiar manner of arranging its 

 eggs, as well as a choice of situation. In every case, how- 

 ever, they are placed within the vivifying influence of the 

 solar rays, and are hatched at the season of the year most 

 advantageous for the growth and the comfort of the fry. 



In other oviparous animals, such as birds, before the eggs 

 can be deposited, a house or nest must be constructed, often 

 consisting of various materials, collected with great labour, 

 and formed with exquisite neatness, which in a few species 

 is lined with the down which they pull from their bodies. 

 In all these cases, obedience to this instinct is cheerfully 

 complied with, however difficult, and any obstacle to prevent 

 the execution of its purposes occasions pain. 



b. In each species securing a supply of suitable food for 

 its offspring. The simplest form in which this law is ob- 

 served, consists in the parent depositing its eggs on those 

 substances which are to serve as food for the young when 

 hatched. This is familiarly displayed in the case of the 

 cabbage-butterfly, which deposites its eggs on the leaves 

 which are afterwards to serve as the food of its caterpillar. 

 In the case of the Oestrus equi, the eggs are deposited in 

 such a situation, that circumstances are likely to occur, by 

 which they shall be conveyed to a proper place for the issu- 

 ing forth of the larva, and for its obtaining a suitable supply 

 of food. The female insect attaches her eggs to those parts 

 only of the horse which are most liable to be licked by the 

 tongue, by which process they are conveyed into the sto- 

 mach. There, they are almost instantaneously hatched, the 

 larva, known by the name of bots, adhere to the coats of the 

 stomach by hooks with which they are provided, obtain 

 food from the juices by which the horse is nourished, and 

 wlKMi mature pass out with the dung, to undergo the future 

 changes of life. 



